(256) Investigation into the Poor Seedling Establishment Trait Associated with Compact Phenotype in PI308916 and Possible Relationship to Apical Hook Formation

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Cucumber PI308916 has a compact growth habit (short internodes and main stem length) due to a single recessive gene cp. We also observed that this PI has lower incidence of Phytophthora fruit rot, likely due to its upright fruit bearing habit. Previous researchers reported that compact cucumber lines derived from PI308916 exhibited the potential for higher yields due to increased planting density. Despite these potentially beneficial traits, efforts to develop PI308916-derived lines were terminated due to poor seedling establishment. The objective of this research is to determine the relationship between the compact phenotype and poor seedling establishment. Short internodes can be caused by deficiency in gibberellins or brassinosteroids that can also impact germination or apical hook formation, a trait important for seedling emergence from the soil. Germination rate and apical hook angle was recorded for `Wautoma' (control inbred line that forms normal apical hook), PI308916, and their F1, F2, and BC progeny. Germinating `Wautoma' seeds showed consistent, large apical hook angles (mean 147), while hook angles of PI308916 were broadly distributed from 0 to 180 (mean 96). F1 progeny for the reciprocal crosses had a similar angle (mean 134 and 133) to `Wautoma'. Segregation ratios for apical hook angle in the F2 and BC populations were consistent with a single recessive gene. Evaluation of the relationship between the apical hook and compact phenotype, showed an absence of the recombinant class of long internodes and small apical hook angle in the F2 population, suggesting that the two traits may be conferred by a single gene or two tightly linked genes.