xx = work needed SEED SIZE IN SESAME

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At the 1998 FAO/IAEA RCM in Thailand Langham (1998B) suggested the alternative to weigh 100 seeds and use that weight without multiplying. By using X.X ...
DRAFT xx = work needed SEED SIZE IN SESAME Background. One of the most important factors in developing sesame as a mechanized crop is the ability to establish good stands using planters over different soil types and different moisture conditions. Farmers cannot be setting and resetting the planter constantly and still get across many acres per day. Therefore, most farmers set the planter to place the seed deeper than may be warranted for most conditions in order to insure that the seed will be in the moisture in all conditions. In addition, there are planters that do not have good depth control, and farmers prefer to err on planting too deep. When the seed is deep, there are two factors that can help in getting good emergence. (1) Additional seed can be planted to help push up through the soil, and (2) the seed size can be larger to provide more push. Once the seed has emerged, there is a second stage to establishing a good stand. The seedlings need to start growing as quickly as possible to cover the ground to compete against weeds and get tall enough to keep from being washed in from heavy rains. The cotyledon size at emergence is critical in the ability of the seedlings to grow quickly. Smaller seed, greater distances to emerge, and greater pressure to push through the soil reduce the size of the cotyledon at emergence. Basically, it is the amount of nutrients in the seed versus the amount of nutrients used to emerge. T. Kobayashi (1980) correlates seed size with seedling vigor. The value of a large seed was demonstrated in the Tipton, Oklahoma, Sesaco nursery in 1997. Because of hot, dry, and windy conditions, the seed was planted deeper than normal. Just prior to the seedling emergence, there was enough rain to crust the soil resulting in about a 60% stand. In reviewing the nursery, it became apparent that the larger the seed, the better the stand. A plant breeder has no control how a farmer plants his seed, but a plant breeder can increase the size of the seed to alleviate the problem. In solving the stand problem by increasing seed size, it is important to determine that another problem is not created. The question is whether larger seed size would be acceptable in sesame markets. Seed size would be a factor in the oil market only if there is a negative correlation between seed size and oil content. [xx Is there a reference for this? Look at Kinman and Yermanos] Some Japanese oil crushers prefer smaller seed. In the tahini market in the Middle East most countries produce large seed, and thus it is assumed that flavor is a more important factor than seed size. In the edible market in the United States medium seed is preferred by McDonald Corporation (the largest user in the US) because of the sizes of the screens used to spread the seed on the buns. Their bakery specification demands 340 to 390 seeds in 1 gram which translates to .29 to .26 grams per hundred seeds. When seeds are used whole in foods, the preferred size depends on the

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nature of the product. Small products use small seed; large seed is preferred for products where the seed is visible; but in most products the size is not important (A. Lewin, personal communication). In the Korean edible market, smaller seed is preferred since it is an indication that it is Korean or Chinese seed (C. Kang, personal communication). This paper examines several issues in seed size in order to determine a strategy for breeding larger seeds. Seed size data. In the sesame literature, seed sizes are often expressed in terms of weight of 1,000 seeds. Most publications use grams to the tenth of a gram, and some data is expressed to the hundredth of a gram. Manual seed counting is very time consuming. In the 1996 FAO/IAEA RCM in Turkey, A. Ashri recommended counting 500 seeds and multiplying by two. At the 1998 FAO/IAEA RCM in Thailand Langham (1998B) suggested the alternative to weigh 100 seeds and use that weight without multiplying. By using X.X for 1000 weights and .XX for 100 weights, there would be a clear indication of the methodology used for weighing. In order to determine the validity of the data from counting just 100 seeds, three lines with seed of different sizes were used to count 1,000 seeds in 10 groups of 100 seeds each. Each sample was weighed. The samples were then joined, and the 1,000 seeds were weighed. The results in Table 1 show that at most there is an error of .02 grams. Table 1. Comparison of weighing 100 seeds versus weighing 1000 seeds. Sample Line 1 Line 2 Line 3 1 .26 .29 .37 2 .27 .29 .38 3 .26 .30 .38 4 .26 .30 .38 5 .26 .31 .37 6 .27 .31 .38 7 .27 .30 .38 8 .27 .30 .39 9 .26 .30 .38 10 .26 .30 .38 Total 2.64 3.00 3.79 1000 w 2.62 2.99 3.80 In order to determine the significance of an error margin of .02 grams for 1000 seeds, Langham (1998B) examined the seed weights of Sesaco varieties planted in three nurseries and within one nursery. This data showed that for the same seed planted in different location that the 100 seed weight could vary from .00 grams to .07 grams for an average of .028 difference for 1000 seeds. Thus the error rate in counting 100 seeds is within the normal variation in the same variety grown under different conditions.

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In papers presented at the 1998 RCM, D. Beech (1999) showed a difference in varieties planted in different locations in Australia. Varieties differed as much as .5 grams per 1,000 seeds. Additional counts on Sesaco varieties were made from nurseries planted from 1988 through 1997. The nurseries were planted in Texas, Arizona, and Oklahoma with latitudes ranging from 31 to 35 degrees. The nurseries were planted from early May to mid July. Some nurseries were fully irrigated, some semi-irrigated, and some rainfed. The rainfed ranged from very little moisture during the growing season through more rainfall than irrigated nurseries. The results are shown in Table 2. W100 represents the average of all the samples. The table provides the lowest and highest 100 weights, the difference between the two, standard deviations, and number of samples that were counted and weighed. Table 2. Comparison of 100 seed weights in Sesaco varieties. Var W100 Low High Dif St Dev Num S01 0.31 0.25 0.36 0.11 0.04 12 S02 0.32 0.25 0.35 0.10 0.03 15 S03 0.26 0.18 0.29 0.11 0.03 17 S04 0.39 0.35 0.44 0.09 0.03 7 S05 0.36 0.24 0.43 0.19 0.05 18 S06 0.28 0.18 0.33 0.15 0.04 10 S07 0.29 0.25 0.32 0.07 0.02 17 S08 0.29 0.25 0.31 0.06 0.02 14 S09 0.28 0.24 0.31 0.07 0.02 12 S10 0.28 0.19 0.32 0.13 0.03 17 S11 0.30 0.22 0.39 0.17 0.03 59 S12 0.37 0.28 0.43 0.15 0.04 10 S14 0.32 0.21 0.36 0.15 0.04 15 S15 0.26 0.21 0.30 0.09 0.03 15 S16 0.29 0.24 0.34 0.10 0.02 47 S17 0.26 0.23 0.30 0.07 0.02 50 S18 0.26 0.22 0.30 0.08 0.02 31 S19 0.27 0.21 0.30 0.09 0.02 18 S20 0.32 0.28 0.36 0.08 0.02 27 S21 0.25 0.20 0.28 0.08 0.02 19 S22 0.36 0.32 0.43 0.11 0.03 23 S23 0.26 0.24 0.30 0.06 0.02 17 S24 0.30 0.27 0.32 0.05 0.01 17 S50 0.29 0.25 0.33 0.08 0.03 10 S51 0.27 0.16 0.31 0.15 0.04 9 S52 0.29 0.23 0.33 0.10 0.03 11 From Table 2, it can be concluded that reporting the 100 weight (W100) provides adequate data to convey seed size. In essence, the reader uses the data to mentally place the seed in size classes and the exact weight is not important. Sesaco uses the following classes:

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Very small Small Medium Large Very large