P. L. Pfahler

Genetic variation for in vitro sesame pollen germination and tube growth

Abstract  In vitro pollen germination and tube length studies are valuable in elucidating mechanisms (germination capacity and rate, tube growth rate) possibly associated with genetic differences in male transmission. On each of two collection dates, the percentage germination and tube length of the binucleate pollen grains from five diverse sesame (Sesamum indicum L.) genotypes were determined at eight times (30, 60, 90, 120, 150, 180, 240, 300 min) after inoculation on a semisolid medium containing 10% (100 g l-1) sucrose (C12H22O11), 0.4% (4 g l-1) purified agar (Fisher Lot 914409), 0.1% (1 g l-1) calcium nitrate [Ca(NO3)2 ⋅ 4H2O] and 0.01% (100 mg l-1) boric acid (H3BO3). Before heating, the pH of the medium was adjusted to 7.0 with a 0.1 N potassium hydroxide (KOH) solution. Over the five genotypes, 5% germination was found 30 min after inoculation and a maximum of 37% germination 120 min after inoculation with no significant changes thereafter. As indicated by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which germination was initiated and maximum germination attained. Over all five genotypes, the tube length was 91 μm 30 min after inoculation, reaching a maximum of 1000 μm 300 min after inoculation. As shown by the highly significant genotype×time after inoculation interaction, the genotypes differed in the time at which tube length was observed and the maximum tube length was attained. Little or no relationship between percent germination and tube length was observed among the genotypes. For both percent germination and tube length, the statistical significance of collection date and its interactions with genotype and time after inoculation indicated that environment in the form of collection date was also an influencing factor. These results indicated that genetic differences among genotypes were present for in vitro germination capacity, germination rate and tube growth rate and that these factors singly or in combination could alter male transmission of genetic elements.

Environmental stability and heritability estimates for grain yield and test weight in triticale

Hexaploid triticale has many advantages over both parental species for both grain and forage production in certain environments. Additional information on environmental stability and heritability would be desirable to develop appropriate selection strategies in the production of superior widely-adapted cultivars. The grain yield of 22 diverse genotypes grown at four ecologically-distinct geographical locations [Quincy, FL, USA (approximate geographical coordinates (AGC) = 30°N 84°W, approximate elevation (AE) = 58 m), Plains, GA, USA (AGC = 32°N 84°W, AE = 76 m), Bozeman, MT USA (AGC = 45°N 111°W, AE = 1458 m), and Aberdeen, ID, USA (AGC = 42°N 112°W, AE = 1360 m)] was measured in two years with winter and spring planting dates only at Bozeman and Aberdeen. Test weight (grain weight in a given volume) was determined for two years at Bozeman and Aberdeen at both planting dates and one year at Quincy. Stability analyses indicated that significant (P < 0.01) variation in means, regression coefficients, and deviation mean squares of the genotypes were present for both characters. Realized heritability (h2) estimates were as follows: grain yield ranged from −0.02 to 0.80 with a mean of 0.57; test weight ranged from 0.63 to 1.05 with a mean of 0.93. The results indicated that substantial genetic variation is present and selection for widely-adapted cultivars would be effective for both characters especially test weight.

Genetic and environmental variation in anther, pollen and pistil dimensions in sesame

Measurements of anther (length, width, depth), pollen grain (percent fertility, polar diameter, equatorial diameter, polar diameter/equatorial diameter ratio, volume) and pistil (stigma length, style length, ovary length, total pistil length, stigma width, style width, ovary width) were taken on 12 diverse sesame (Sesamum indicum L.) genotypes on each of four collection dates in 1994. Highly significant differences among genotype means were obtained for all characters except polar diameter. Highly significant differences among environment (collection date) means were found for ten of the 15 characters measured. Highly significant genotype x environment interactions were obtained for all characters except anther length. For the anther characters measured, relatively high repeatability values were found, ranging from 99.8% for length to 87.6% for depth. For the pollen grain characters measured, the repeatability values ranged from 67.6% for percent fertility to 23.1% for polar diameter. For the pistil characters measured, the repeatability values ranged from 94.0% for style width to 49.6% for total pistil length. These results indicate that genotype and environment influence anther, pollen grain and pistil characters. Variation in some of these morphological aspects could influence the consistency and interpretation of male transmission studies on both the applied and evolutionary levels.

Genotypic effects on pollen morphology in sesame (Sesamum indicum L.)

SummaryThe morphology (shape, exine wall pattern, diameter, volume, surface area) of mature pollen grains from eight genotypes, four within each of two capsule types (dehiscent, indehiscent) was studied. The shape was a flattened sphere (oblate) with a P (polar axis diameter): E (equatorial axis diameter) ratio = 0.69. The exine wall pattern consisted of a series of furrows passing through the poles and intersecting the equatorial plane at right (90°) angles. In cross section, the furrows appeared to be associated with shallow U-shaped structures with the intine protruding between these structures. Over the eight genotypes, the diameter, volume, and surface area were 65 μm, 147300 μm3, and 13444 μm2, respectively. For all three related characters, highly significant differences between capsule type and genotypes within capsule type were obtained. For each character, the dehiscent capsule type mean was larger than the indehiscent capsule type mean with minimum overlap among the four genotype means within each capsule type. Possibly, the numerous and diverse pleiotropic effects associated with this simply-inherited recessive indehiscent capsule type character includes pollen dimensions.