Light Effect on Seed Chlorophyll Content and Germination Performance of Tomato and Muskmelon Seeds
The stage of maturity of seeds at harvest is an important factor that determines seed vigor. Separating seeds from a seed lot composed of many different stages of development can be difficult especially after maximum dry mass is attained. Separating seeds based on their physiological maturity is more challenging than sorting seeds based on their physical properties. Seeds may be non-destructively sorted using chlorophyll fluorescence (CF) as a marker of seed maturity. This study was conducted to test whether CF could be used to remove low vigor immature seeds from muskmelon (Cucumis melo L.'Top Mark') and tomato (Lycopersicum esculentum) seed lots. Light treatments were applied to determine whether the light environment during seed harvesting and processing could affect chlorophyll content and seed vigor. Seeds from nine stages of development were collected from 'TopMark'. Seeds from three stages of fruit development (red ripe, breaker, and mature green) were harvested from tomato cultivar Money Maker and two phytochrome mutants: phytochrome A mutant, fri-1 and phytochrome B mutant, tri-1. The SeedMaster Analyzer (Satake USA Inc., Houston Texas) was used to measure CF and to sort individual seeds according to CF levels. Immature tomato seeds and muskmelon, harvested from green fruits, had the highest CF (p>0.001). Contrary to the results obtained with the other tomato genotypes, the vigor of tri-1 did not change inversely with changing CF levels, rather, seeds with low CF had the same vigor as seeds with high CF. This result may suggest that the presence of phytochrome B exerts an inhibitory influence on vigor in tomato seeds, and that the persistent presence of chlorophyll during seed development does not affect vigor. The light treatments had no consistent effect on seed chlorophyll content or on vigor in either tomato or muskmelon.