Triploid or seedless watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] cultivars often have erratic germination and low seedling vigor. The morphology of the seedcoat on two triploid cultivars—Tri X 313 and Tri X Sunrise—was examined by scanning electron microscopy (SEM) to identify structural differences compared to diploid seeds. Triploid seeds incubated with oxygen-enhanced treatments that included nicking, 1% hydrogen peroxide (H2O2), and 40% oxygen were investigated at low and high medium moisture levels. Triploid seed has a thicker seedcoat with a dense endotesta layer and a larger and highly variable air space surrounding the embryonic axis as compared with diploid seed. All cultivars rapidly imbibed water (≈50% of the original weight) during the first hour of imbibition, with a faster increase for triploids than for diploids. High moisture affected germination to a lesser extent in diploid than triploid seeds. Triploid germination under low medium moisture ranged from 96% to 76%, but was severely reduced to <27% under high medium moisture. Triploid seed germination was significantly improved at high moisture by H2O2 and by 40% oxygen. Triploid watermelon seed is very sensitive to submerged conditions, possibly due to a combination of physiological and morphological defects. The rapid imbibition and excess water collected in the seedcoat and air space surrounding the embryo, could reduce oxygen diffusion and impair metabolic pathways leading to normal germination and seedling development.
Stacie Grange, Daniel I. Leskovar, Leonard M. Pike, and B. Gregory Cobb
Sat Pal Sharma, Daniel I. Leskovar, Kevin M. Crosby, and A.M.H. Ibrahim
The stability of yield and quality traits in nine orange-fleshed melon (Cucumis melo L.) genotypes was studied over nine environments in south-central Texas (College Station, Uvalde, and Weslaco) over 3 years (2010, 2011, and 2012). Besides yield traits, fruit -quality components such as soluble solids content (SSC), β-carotene, and fruit firmness were also measured. Data were subjected to the combined analysis of variance and trait stability by GGE Biplot. The significant genotype-by-location interactions for yield traits demonstrated the potential to develop location-specific cultivars. However, the temporal fluctuations in productivity emphasized the need to select for stability over several years in potential cultivars for the target environments. Cultivar Mission was confirmed as the most stable and average performing genotype for marketable yield and quality traits at all locations. Uvalde was identified as the ideal location for selecting generally adapted genotypes for south-central Texas. Biplot analysis indicated that Orange Dew was the highest mean performing genotype for SSC. The hybrid Oro Duro, followed by TAMU 146, ranked highest for mean and stability of β-carotene content, but it ranked lowest for fruit firmness. TAMU Orange Casaba exhibited specific adaptation, producing the highest mean fruit yield at Weslaco, while Journey had the highest fruit yield at College Station and Uvalde. Understanding of genotype-by-environment interactions for multiple traits in melon is critical for developing cultivars with high mean performance and stability in target growing environments.
Justin D. Butcher, Kevin M. Crosby, Kil Sun Yoo, Bhimanagouda S. Patil, A.M.H. Ibrahim, Daniel I. Leskovar, and John L. Jifon
Habanero peppers have become increasingly popular in the United States for supplying unique flavors and high levels of pungency. As consumption of this product increases, development of improved cultivars with elevated phytochemicals will likely result in additional demand from consumers. This study evaluated fruit size, capsaicinoid, and flavonoid concentrations in six Habanero (Capsicum chinense) genotypes grown at three different Texas locations: College Station, Uvalde, and Weslaco. Five of these Habanero experimental hybrids (H1-red, H2-orange, H3-orange, H5-dark orange, and H6-yellow) were developed at Texas A&M University with genetic improvement in numerous traits of interest, and Kukulkan F1 (Kuk-orange) was included as a commercial control. In general, H1-red had the largest fruits in these locations. Capsaicin and dihydrocapsaicin (DHC) concentrations were highest in Kuk-orange followed closely by H5-dark orange and were lowest in H6-yellow. Fruit at Weslaco was larger and contained more capsaicin and DHC than those produced in Uvalde or College Station. Although flavonoid contents were variable and low in all genotypes and locations, H3-orange showed the most stability for use in future crossing schemes to compete against Kuk-orange for this characteristic. Our results suggest that variation in phytochemicals in fruit tissue of Habanero genotypes can be exploited by selecting in an appropriate environment.