In higher plants, cell-cell recognition reactions taking place following pollination allow the selective restriction of self-pollination and/or interspecific pollination. Many of these systems function by regulating the process of water transfer from the cells found at the stigmatic surface to the individual pollen grain. Interspecific pollination studies on the cruciferous weed Arabidopsis thaliana revealed only a broad specificity of pollen recognition such that pollen from all tested members of the crucifer family were recognized, whereas pollen from almost all other species failed to hydrate. Genetic analysis of A. thaliana has identified three genes that are essential for this recognition process. Recessive mutations in any of these genes result in male sterility due to the production of pollen grains that fail to hydrate when placed on the stigma, but that are capable of hydrating and growing a pollen tube in vitro. Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen-stigma recognition system. All three mutations described also result in a defect in the wax layer normally found on stems and leaves, similar to previously described eceriferum (cer) mutations. Genetic complementation and mapping experiments demonstrated that the newly identified mutants are allelic to the previously identified genes cer1, cer3 and cer6. TEM analysis of the ultrastructure of the pollen coating revealed that all of the mutant pollen grains bear coatings of normal thickness and that tryphine lipid droplets are missing in cer1-147, are reduced in size in cer6-2654 and appear normal in cer3-2186.(ABSTRACT TRUNCATED AT 250 WORDS)

Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to characterize genetic relationships among 46 accessions in two C. melo L. subsp. melo (Cantalupensis, Inodorus) and subsp. agrestis (Conomon and Flexuosus) groups. Genetic distance (GD) estimates were made among and between accessions in four melon market classes [Galia, Ogen, Charentais, and Shipper (European and U.S. types)] of Cantalupensis, one market class of Inodorus (Cassaba and Honey Dew), one accession of Conomon, and one accession of Flexuosus by employing three GD estimators; simple matching coefficient, Jaccard's coefficient, and Nei's distance-D. Differences detected among 135 RAPD bands and 54 SSR bands (products of 17 SSR primers) were used to calculate GD. Band polymorphisms observed with 21 RAPD primers and 7 SSR primers was important in the detection of genetic differences. Estimators of GD were highly correlated (P > 0.0001; rs = 0.64 to 0.99) when comparisons were made between estimation methods within a particular marker system. Lower correlations (P > 0.001; rs = 0.17 to 0.40) were detected between marker systems using any one estimator. The GD of the Conomon and Flexuosus accessions was significantly different from the mean GD of all the market classes examined, and market classes were distinguishable from each other. Although lower coefficients of variation can be attained in the estimation of GD when using RAPDs compared to SSRs, the genetic relationships identified using these markers were generally similar. Results of RAPD marker analysis suggest that 80 marker bands were adequate for assessing the genetic variation present in the accessions examined.

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Reduced palmitate content in soybean [Glycine max (L.) Merr.] is controlled by two major alleles, fap1 and fap3. This study was conducted to determine the role that modifying genes may have on the reduced palmitate trait in lines homozygous for the major alleles. Two lines homozygous for fap1 and fap3, AX5152‐34 and AX5152‐105, were each crossed as donor parents to a high‐yielding cultivar with normal palmitate, ‘Kenwood’ or ‘Marcus’. The F1 plants were backcrossed to the high‐yielding cultivar. Two experiments were grown in randomized complete‐block designs at three locations in Iowa with two replications per location. The Kenwood experiment consisted of 14 F4:6 lines from the cross AX5152‐105 × Kenwood, 83 BC1F3:5 lines from five BC1 families from the backcross Kenwood × (AX5152‐105 × Kenwood), Kenwood and AX5152‐105. The Marcus experiment contained 14 F4:6 lines from the cross AX5152‐34 × Marcus, 69 BC1F3:5 lines from the backcross Marcus × (AX5152‐34 × Marcus) among six backcross families, Marcus and AX5152‐34. All lines, except Kenwood and Marcus, were homozygous for both fap1 and fap3. The influence of modifying genes on palmitate content was evident in both experiments. There were significant differences in palmitate content among single‐cross lines, among backcross lines, and among lines within individual backcross families. The palmitate content of each donor parent was significantly different from the means of the corresponding single‐cross and backcross populations. Lines with reduced palmitate were obtained that had higher yield than the recurrent parents, which indicated that reduced palmitate is not detrimental to yield. Lines with reduced palmitate generally had reduced oil content.