MXPA96003125A - Seed value through defiolation before the harvest of plants of m - Google Patents

Abstract

The present invention achieves an increase in the quality of the corn seed, especially with respect to a better vigor of the seed, by defoliation of the corn plants during a specific period after the pollination. Then an assembly of corn seeds is obtained which is characterized by a better vigor of the seed

Description

VIGOR OF SEED THROUGH DEFIOLATION BEFORE THE HARVEST OF CORN PLANTS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for improving the quality of corn seeds. In particular, this invention relates to a method for improving the vigor of corn seeds by defoliating maize plants after pollination. This invention also relates to an assembly of corn seeds characterized by an increased seed strength, which can be obtained using the method described. 2. Background The quality of the seed is of great concern in agriculture around the world. The quality of the seed is subject to legislative control and certification schemes in most developed countries. Forbes et al., PLANTS IN AGRICULTURE, Cambridge University Press (1992). In subsistence farming systems, especially in the developing world, the poor quality of the seed is a major constraint to productivity. Id.

An important factor in the determination of the quality of the corn seed is the maturity of the seed at the time of harvest. Often, the corn seed is harvested before the seed reaches optimum maturity. 5 The reasons for a premature harvest include risk of freezing, capacity of the production plant, and the need for time to move the seed from the production site in the southern hemisphere, to a plantation site in the northern hemisphere. In addition, many varieties of lft grafted corn lines do not ripen uniformly throughout the field, resulting in a seed crop containing a seed of poor quality. Seed quality is typically measured by standard germination tests. Delouche and collaborators, Proc. Assoc. Off. Seed Anal. 50: 124 (1960); Woodstock, Seed World 97: 6 (1965). Although the results of a standard germination test can correlate well with emergence in the field when soil conditions are favorable for rapid emergence, the test does not can predict field performance when soil and environmental conditions impose stress on germinating seeds, as often happens with early planting. Tekrony et al., Crop Sci. 17: 573 (1977). 25 The concept of "seed vigor" evolved to compensate for the failure of standard germination tests to predict the operation of the field under conditions of environmental stress. Adegjuyi et al., J. Agron. & Crop Sci. 161: 111 (1988). The vigor of the seed is a reflection of the properties that determine the potential for a rapid and uniform emergence of the plants, and the development of normal seedbeds under a wide range of field conditions. 1983 SEED VIGOR TESTING HANDBOOK (Assoc. Official Seed Analysts). It is thought that the vigor of the seed has influence not only on the emergence and the speed of emergence, but also on the height of the plant, the diameter of the stem, the dry matter of the stem, the length of the leaf, and the width of the sheet. Adegbuyi et al., J. Agronomy & Crop Science 161: 111 (1988). The quality of the vigor of the seed is particularly important where there is a crop near the limits of its climate tolerance range, or it is sown under adverse conditions of the soil. In the corn belt of the northern United States, and in Europe, maize is generally planted in early spring in soils that are, or may become, too cold and humid for optimal germination. Accordingly, there is a need for a method to increase the quality of the corn seed, as measured by the vigor of the seed. There has been an extensive study of the effects of the defoliation of the crop on the yield and quality of the seed. See, for example, corn: Hicks et al., Agronomy J. 69: 381 (1977), Tollenaar et al., Can. J. Plant Sci. 58: 207 (1978), Crookston et al., Crop Sci. 5 18: 485 (1978), Johnson, Agronomy J. 70: 995 (1978), Hunter et al., Crop Sci. 31: 1309 ( 1991); sunflower: Prokof'evy collaborators, Prik. Biokhimiya Mikrobiol. 8: 402 (1972); soybeans: Mesa et al., Crop Sci. 24: 847 (1984), Vieira et al., Crop Sci. 32: 471 (1992); sorghum: Onofre Q et al., Agroscience 65: 253 (1987); lime seed: Coggin et al., J. Econ. Entomol 73: 609 (1980). See also Saleh et al. In 1974 YEARBOOK, Indonesian Central Institute for Agriculture (rice, maize, sorghum, peanut, and soybeans). The overall tenor of this body of literature 5 is that defoliation, although unavoidable and harmful in certain contexts, can actually have a desirable effect, for example, with respect to the greater 'oil content / yield of sunflower seeds.

Prokof 'ev et al., Supra. 0 Furthermore, Crookston et al., Supra, report that defoliation can improve performance in short-season maize hybrids. Crookston et al. Found that although leaf removal during stigma formation consistently led to a reduction in maximum yield, defoliation at a very early growth stage, before flowering, improved yield. However, it has not been possible to predict whether defoliation before flowering could provide better seed vigor, since the yield and vigor of the seed are not clearly correlated in the maize. Adegbuyi et al., J. Agronomy and Crop Science 162: 10 (1989).

SUMMARY OF THE INVENTION In accordance with the foregoing, it is an object of the present invention to improve the overall vigor of the seed harvested in a crop by defoliating the crop during a critical period. It is a further object of the present invention to produce a more uniform maturation of the seed in a population of corn plants to improve the vigor of the harvested seed. These and other objects are achieved, in accordance with one embodiment of the present invention, by the provision of a method for the treatment of a group of corn plants, which comprises the steps of: (A) reducing the functional leaf area substantially in all plants, where the reduction in the functional leaf area is made between about 600 and about 850 days of growth rate after pollination of the plants, and then (B), harvesting the group, in such a manner that an assembly of seed of the group is obtained which is characterized by a level of seed vigor that is improved in relation to the level of seed vigor in a seed assembly harvested from a comparison group of maize plants not subject to reduction of functional sheet area. In accordance with another embodiment of the present invention, an assembly of corn seed is provided which is characterized by a greater vigor of the seed.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES There is little description in the literature regarding the effect of defoliation on the vigor of the seed. In a rare study on seed vigor, Vieira et al., Supra, found that defoliation of soybeans resulted in underdeveloped seeds characterized by reduced germination and seed vigor. In striking contrast to the negative findings of Vieira and coworkers, the present inventors made the surprising discovery that defoliation can be used as a tool to obtain a better corn seed vigor by properly balancing the maturity obtained from the seed and a smaller seed size. However, the inventors discovered that defoliation must be performed during a critical period in the maturation of the corn crop, as described herein. In accordance with the invention, a group of corn plants is treated to reduce the functional leaf area substantially in all plants. A "group" refers to a living assembly of corn plants. A group can be quantified by determining the total dry mass of corn plants in an area. The "functional leaf area" of a plant refers in the present description to the total area of the leaf that is capable of intercepting sunlight. The functional leaf area is reduced by removing all the leaves from the plants, or by removing all the leaves above the spike, including the spike blade. "Substantially all plants" is referred to in the present description to at least 99 percent of the corn plants in the group. In the present context, "seed assembly" denotes a collection of seeds harvested from a group of corn plants. The methodology of the present invention can be used to produce a seed crop characterized by increased seed vigor, determined by a seed vigor test. "Seed vigor" refers to a collection of properties that determine the potential for a rapid and uniform emergence of plants, and the development of normal seedbeds under a wide range of field conditions. The degree of vigor of the seed possessed by a given seed assembly can be determined by a variety of techniques. 1983 SEED VIGOR TESTING HANDBOOK, supra. For example, the vigor of the seed can be determined by observing the early count of the group, or by observing the amount of the vegetative group produced by the seeds after emergence in the seedling stage, as described in Example 2 herein. Alternatively, the vigor of the seed can be assessed using an in vitro germination test. For example, the Pioneer Cold Test can be used to predict how corn seed will work in a cold environment and wet. See Martin et al., Crop Sci. 28: 801-805 (1988), and Example 1 below. The soak test is an alternative in vitro germination test that can be used to identify inbred lines that are less cold tolerant. Martin and collaborators, supra. Briefly, the soaking test is done by soaking the seeds in deionized water, and then the seeds are spread between two pieces of heavy germination paper. The extended seeds are incubated for 5 days at 27 ° C, and the germinated seeds are counted.

The present inventors discovered that defoliation of corn plants can improve the vigor of the seed if the defoliation was carried out during a particular period after pollination. Defoliation after the critical period will not produce an improvement in seed vigor, while defoliation before the critical period will result in an unacceptable reduction in seed size. This critical period is determined by measuring the "days of degree of growth" (DGC). The system of "days of degree of growth" is a standard among systems to assess maturity in corn. See, for example, Eckert et al. In 1986 NATIONAL CORN HANDBOOK, page 1017. The significance of growth grade days is that a certain number of growth grade days are taken for an endogamous or hybrid to reach a particular stage of growth. plant development. As used herein, the days of degree of growth are calculated by the Barger Method, where the heat units are calculated over a period of 24 hours by using the formula: (Maximum ° C + Minimum ° C ) DGC = -50. 2 Barger, Weekly Weather Crop Bulletin 56:10 (May 5, 1969).

In accordance with the present invention, defoliation must be carried out from about 600 days of growth grade after pollination, to about 850 days of growth grade after pollination. In general, the degree of improvement of seed vigor is inversely related to the number of days of degree of growth after pollination at the time of defoliation. Therefore, the greatest improvement in seed vigor can be obtained by lt, defoliation at 600 days of growth grade after pollination, which is the earliest time in the window of 600 to 850 days of degree of increase. However, the cost of increased seed vigor induced by this early defoliation is a potential decrease in the seed size. The size of the seeds in a corn seed crop is an important commercial consideration, because the largest seed size on the market is preferred. Therefore, the precise time of the selected defoliation will reflect a balance between the desired improvement in the seed vigor and the desired seed size. Since the genotype determines the maturation rate of the corn seed and the rate of increase in the size of the seed, the time of defoliation must be determined for each particular corn hybrid. In general, hybrids that bloom earlier tend to have seeds that increase in size and mature quickly. Table 1 provides a general guideline for selecting the time of defoliation. Typically, defoliated plants provide a corn seed crop characterized by increased seed vigor and a loss in seed size of approximately 10 percent, as measured by the dry weight of the seed.

TABLE 1 GUIDELINES FOR SELECTING THE TIME OF DEFILE DGC at flowering Defoliation time (DGC after pollination) 1100 600 1200 650 1300 700 1400 750 1500 and then 800 In accordance with the present invention, defoliation can be carried out by a variety of methods. For example, defoliation can be done by a mechanical element. One method of defoliation is manual defoliation, as illustrated in Examples 1 and 2 below. Alternatively, defoliation can be performed employing the application of chemicals, such as a herbicidal formulation. Any herbicide can be used for a herbicidal formulation in the practice of the present invention. Preferred herbicides include herbicides that: (1) are characterized by low residual toxicity, (2) do not translocate to the spike, and (3) are effective as defoamers in a variety of environmental conditions. Examples of herbicides that are suitable for a herbicidal formulation include Paraquat, 1, 1-dimethyl-4,4'-dipyridinium (ICN Biochemicals, Inc.); Roundup®, mono- (isopropyl amine) salt of N- (phosphonomethyl) glycine (Monsanto Chemical Company); Ignite®, monoammonium 2-amino-4- [(hydroxy) methyl-phosphinyl] -butanoate (Hoechst-Roussel Agri-Vet Company); and Diquat, 1, l'-ethylene-2, 2'-dipyridinium (Valent U.S.A. Corporation). Preferred herbicides include Paraquat, Ignite® and Diquat. In the practice of the present invention, the plants are treated with herbicides according to the instructions of the manufacturers. Typical modes of application of the herbicide are illustrated in Examples 2 and 3 below. A herbicidal formulation may also include a surfactant to improve the recovery of the herbicide by the corn plant. Examples of the anionic surfactants include calcium and amine salts of dodecylbenzenesulfonic acid and sodium diisoethyl sulfosuccinate. Examples of the cationic surfactants include aliphatic mono-, di-, or poly-amine such as an acetate or oleate. Nonionic surfactants are preferred. Examples of the nonionic surfactants include the condensation products of fatty acid esters, fatty alcohols, fatty acid amides, or fatty amines with ethylene and / or propylene oxide, phenols substituted by alkyl, alkenyl, or polyaryl with ethylene and / or propylene, and fatty esters of polyhydric alcohol ethers, such as sorbitan fatty acid esters, condensation products of those esters with ethylene oxide, including polyoxyethylene sorbitan fatty acid esters, oxide block copolymers of ethylene and propylene oxide, ethoxylated lanolin alcohols or ethoxylated lanolin acids. Representative nonionic surfactants include PG 26-2®, a secondary butyl (((phenoxy (polypropylene) oxy) polyethylene) oxy) ethanol (The Dow Chemical Company); Silwet L-77®, a non-ionic silicone glycol copolymer (Union Carbide Corporation); and Triton (Ortho) X-77®, alkylaryl polyoxyethylene glycol (Chevron Chemical Company). X-77® is a particularly preferred surfactant. The selection of a suitable surfactant is well within the capabilities of an expert in this field. The amount of surfactant present in a concentrated herbicidal composition will generally be in the range of from about 0 percent to about 5 percent, preferably from about 0 percent to about 0.5 percent by weight of the final herbicidal formulation . The present invention, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration, and are not intended to be limiting of the present invention.

Example 1 Effect of Manual Defoliation at 600 Days of Growth After Pollination on Seed Vigor In these studies, fifteen inbreds were grown in isolated fields in Willmar, Minnesota. The inbreds 0 included: R19, W03, 63, 76, W80, G50, J40, P02, M63, K74, W86, MIO, G47, and W06. In the experimental groups, defoliation was carried out after 600 days of growth after pollination by manually separating all the leaves of the plants. The control groups did not decay.

The effect of defoliation on the maturation of the seed was evaluated using either the milk line method or by observing the appearance of the black layer of the seed. The milk line method for determining seed maturity is based on the progressive solidification of the milky endosperm that starts at the apex of the seed and ends at the base of the seed. For example, the milk line is present at about a quarter of the way down from the apex at the 75 percent stage of the milk line, while the milk line is present at the midpoint of the seed at the 50 percent stage of the milk line. The disappearance of the milk of the seed is coincident with the termination of the increase of the dry weight of the seed and the physiological maturity. The black layer method for evaluating seed maturity is based on the development of a black layer in the placental-chalazal region of the seed. The appearance of the black layer indicates the end of the maturation of the seed. To evaluate the effects of defoliation on seed vigor, the seed was harvested at 100-day intervals of growth grade from 600 days of growth grade after pollination to 1000 days of growth grade after pollination. The quality of the seed was examined using the Pioneer Cold Test.

Martin et al., Crop Sci. 28: 801-805 (1988). Briefly, the Cold Test was performed by uniformly distributing a thin layer of sand-loam soil on wet germination paper, and then, the soil and the germination paper were cooled to 10 ° C for 24 hours. The soil and the germination paper were kept moist by wicks of cloth that were spread from the paper to a water tank. Four replicates of the test seeds were placed with the embryo side down on the soil, and the seeds were incubated at 10 ° C for 7 days. Then, the seeds were transferred at 27 ° C and 85 percent relative humidity for 3 days. The vigor of the seed was determined by calculating the percentage of germinated seeds. The results of these experiments showed that defoliation at 600 days of growth grade increased the speed of seed maturation. The non-defoliated control inbreds reached the stage of 75 percent of the milk line at 760 days of growth after pollination, while the defoliated inbreds reached the 75 percent stage of the milk line at 700 days of growth grade after pollination. The control inbreds reached the stage of 50 percent of the milk line at 840 days of growth grade after pollination, while the defoliated inbreds reached the same stage at 770 days of growth after pollination . In a similar way, the non-defoliated control inbreds reached the black layer stage at 960 days of growth grade after pollination, while the defoliated inbreds reached the black layer stage at 890 days of growth grade. after pollination. Therefore, defoliation increased the seed maturation rate by approximately 70 days of growth grade, which was the equivalent of 6 to 8 days under the conditions of this study. In addition, the results of the Cold Test showed a better vigor of the harvested seeds of the defoliated plants, compared with the seeds harvested from the non-defoliated control plants. See Table 2. Accordingly, defoliation at 600 days of growth grade after pollination provided a better seed vigor, as well as an increase in the speed of seed maturation.

TABLE 2 VIGOR OF SEED AT 700-1000 DAYS OF GROWTH AFTER POLLINATION, MEASURED BY PIONEER COLD TEST Results of the Cold Test (% of Germination) Endogamous: 700 800 900 100 Treatment DGC DGC DGC DGC le »R19: Control 59 65 92 87 Defoliation 63 82 94 95 W63: Control 60 77 79 73 Defoliation 51 76 91 90 K76: Control 20 41 86 82 Defoliation 25 74 93 88 W80: Control 38 87 92 83 Defoliation 59 93 95 95 Example 2 Effect of Manual and Chemical Defoliation at 750 or 850 Days of Growth Degree After Pollination on Seed Vigor In these studies, 20 Inbred as females in two isolated fields of Kekaha, Hawaii. One field contained a male W52 and the following females: M49, G29, 30, R03, MJ8, V78, BW6, N46, W78, and AB6. The other field contained a male P03 and the following females: W52, K29, W61, UNCLE, P85, R41, JOl, K35, AB5, and HRl. Both isolated fields were planted on November 19, and all inbreds were forming stigmas on January 17. The days of growth grade after pollination were counted beginning on January 20. The control groups did not defoliate. In the experimental groups, the plants defoliated at approximately 750 and approximately 850 days after the pollination. Defoliation was done by separating the leaves manually or by chemical treatment. Manual defoliation was performed by breaking the flag leaf of the mid rib to the nodule of the spike. Chemical defoliation treatments included: 680.4 grams of Paraquat (ICN Biochemicals Inc.) / acre, or 425.25 grams of Roundup® (Monsanto Chemical Co.) plus 0.568 liters of X-77® (Chevron Chemical Company) / acre. The chemicals were applied using a John Deere 6000 Hi cycle sprayer, with two spray nozzles measuring 71.12 centimeters in length, one nozzle on a row, 11,004 flat fans of 2.1 kg / cm2 at a spray speed of 3.5 mph. 75,708 liters of water were used per 0.264 acre. To test the effects of defoliation on the vigor of the seed, the seed was harvested either at maturity of the seed or before the maturity of the seed. Corn seed groups were harvested to maturity as determined by observing the formation of the black layer. In these studies, the black layer stage occurred at 1,120-1,200 days of growth grade after pollination. At this stage of maturation, 20 to 28 percent of the endosperm was solid, determined by a GAC II moisture meter (Dickey-John). In the group of corn harvested early, ears were harvested at the 50 percent stage of the milk line. In these studies, the 50 percent stage of the milk line occurred at 906-1050 days of growth after pollination. At this stage of maturity, 35 to 40 percent of the endosperm was solid, determined by a GAC II moisture meter (Dickey-John). The quality of the seed was tested using a field emergence test. In these studies, the seeds were planted on April 5 in a greenhouse in Johnston, Iowa, as three replicates of 50 seeds. The average daily high temperature was 15.5 ° C, and the daily low 5 was 5 ° C before emergence. The first emergence was recorded on April 30, which was at 190 days of growth after planting. The early group count and seedling vigor were recorded in stage V3, where the seedling "-, presented three fully expanded leaves.The early group count was calculated as the number of surviving plants. using a visual evaluation of one to nine of the amount of vegetative growth after emergence in the seedling stage where the plant typically contains approximately five leaves.A higher grade indicates a better vigor.The evaluation of seedling vigor is based in a judgment of the uniformity of emergence, the height of the plant, and the mass of green leaf tissue. 0 The dry weight of the seed was calculated by drying the seeds for 72 hours at 104 ° C in an oven. The weight was recorded from two replicates of 20 seeds. The results of these studies show that the early group count declined significantly in the early harvest. As shown in r 'Tables 3 and 4, the global early group count for the black layer harvest was 75 percent, compared with 60 percent for the early harvest in the 50 percent line stage milk. In addition, the early harvest reduced seedling vigor from a value of 4.9 (black layer harvest) to a value of 4.5 (harvesting half of the milk line). However, the damaging effects of early harvest on the early group count were overcome by defoliation at 850 days' growth rate, either by manual or chemical defoliation, as shown in Table 4. Dry weight of the seed harvested from the defoliated plants was only 4 percent less than the dry weight of the seeds harvested from the non-defoliated plants, indicating that the effect of defoliation on seed size was minimal.

TABLE 31 ANALYSIS OF THE SEED REAPPED ON THE DATE OF THE BLACK CAPE Time Count Method of Vigor Weight Defoliation Defoliation Dry Group (DGC) Early (%) Semillero Semill (grams) Control --- 75 4.9 5.4 Manual 750 73 4.9 4.4 850 78 5.1 4.9 Paraquat 750 71 4.6 4.7 850 78 5.0 5.0 Roundup 750 74 4.8 4.8 850 77 5.1 5.2 • -The defoliation time was measured from the date of pollination (full stigma). The early group count, the seedling vigor, and the dry weight of the seed were determined as described in the text.

TABLE 41 ANALYSIS OF THE SEED REAPPED IN THE STAGE OF 50 PERCENT OF THE MILK LINE Time Count Method of Vigor Weight Defoliation Defoliation Dry Group (DGC) Early (%) Seedbed Seed (grams) Control 60 4.5 5.1 Manual 750 71 4.6 4.4 850 71 4.8 4.9 Paraquat 750 63 4.5 4.6 850 67 4.6 4.9 Roundup 750 68 4.6 4.7 850 67 4.8 4.9 - * The defoliation time was measured from the date of pollination (complete stigma). The early group count, the seedling vigor, and the dry weight of the seed were determined as described in the text.

These results indicate that the defoliation before the corn harvest at 850 days of growth degree, either manually or with a herbicidal treatment, significantly improved the emergence in the field of corn harvested before the layer stage black, while only a minimal decrease in seed size was caused.

Example 3 Effect of Defoliation with Ignite® or Diguat at 732 or 755 Degree Days of Growth on Seed Vigor In this study, inbred fields were planted in Johnston, Iowa. The inbred, K76, was planted on May 4, while the inbred T47 was planted on 30 May. of April. Chemical defoliation was performed using either 172,368 grams of Diquat active ingredient (Valent U.S.A. Corporation) / acre, or 190,512 grams of Ignite® active ingredient (Hoechst-Roussel Agri-Vet Company) / acre. The chemicals were applied using a high-reach sprayer with two spray nozzles in 15.24 meter strips, covering two rows per strip. 132,489 liters of water per acre were used. Field K76 was sprayed on September 11 at 732 days of growth grade after pollination, and was harvested 7 days later at 856 days of growth grade after pollination. Field T47 was sprayed on September 3 at 755 days of growth grade after pollination, and was harvested 13 days 5 later at 992 days of growth grade after pollination. In these studies, chemical defoliation had the greatest impact on the quality of the K76 seed. The Ignite ® and Diquat improved the germination of the Cold Test of the K76 - seed by 21 percent and 19 percent, respectively. The Cold Test germination values for the T47 seed improved 8 percent with the Ignite® treatment, and 4 percent with the Diquat treatment. Therefore, the quality of the seed improved by defoliating before harvest using either Ignite® or Diquat.

Although the foregoing refers to the particular preferred modalities, it will be understood that the present The invention is not limited in that way. The ordinary experts in this field will think that different modifications can be made to the described modalities, and that those modifications intend to be within the scope of the present invention, which is defined by the claims following.

All publications and patent applications mentioned in this specification indicate the level of capability of those in the field to which the invention belongs. All publications and patent applications are hereby incorporated by reference to the same extent as if each individual publication or patent application was indicated in a specific and individual manner to be incorporated as a reference in its entirety.

Claims (8)

1. A method for the treatment of a group of corn plants, which comprises the steps of: (A) reducing the functional leaf area substantially in all plants, wherein this reduction is made between about 600 and about 850 days of degree of growth after the pollination of these plants, and then (B), harvest the group, in such a way that an assembly of seeds is obtained from this group, which is characterized by a level of vigor of the seed that is improved in relation to the level of seed vigor in an assembly of seeds harvested from a comparison group of maize plants not subject to that reduction of the functional leaf area. The method of claim 1, wherein the functional sheet area is reduced by a mechanical element. 3. The method of claim 1, wherein the functional sheet area is reduced by a chemical element. 4. The method of claim 3, wherein the chemical element comprises a herbicidal formulation. The method of claim 4, wherein the herbicidal formulation comprises a herbicide that is selected from the group consisting of Paraquat, Ignite, ®, Diquat, and Roundup®. 6. The method of claim 5, wherein the herbicidal formulation comprises Ignite®. The method of claim 4, wherein the herbicidal formulation further comprises a surfactant. 8. An assembly of corn seeds having a better vigor of the seed, wherein the assembly of seeds is obtained by the method of claim 1.