Diploid‐Tetraploid Comparisons in Rye. III. Temperature Effects on Seedling Development1

The late fall planting season for rye in the southeastern USA is typically characterized by an extreme range of temperature conditions. The potential for selection of diploid and tetraploid rye (Secale cerealeL.) populations possessing superior seedling growth characters over a broad range of temperatures was assessed by examining the effect of genetic background on various seeding growth characters at three temperatures (12, 20, 28°C). Diploid populations, and their colchicine‐derived tetraploid counterparts from five genetic backgrounds (‘Elbon’, ‘Explorer’, ‘Florida Black’, ‘Gator’, ‘Wrens Abruzzi’) were compared. The seedling characters included shoot and primary root growth day−1, root cross‐sectional area at the meristematic region, and primary root bluntness ratio (distance from the plane of maximum root diameter at the meristematic region to the root tip divided by the maximum root diameter at the meristematic region). Highly significant ploidy level (PL), genetic background (GB), and temperature (T) main effects were obtained for both shoot and primary root growth day−1. A highly significant T✕GB✕PL interaction was found for shoot growth day−1, but this effect was not significant for root growth day−1. The T ✕ PL interaction was significant for primary root growth day−1at the 0.05 level. Highly significant ploidy level (PL) and temperature (T) main effects were obtained for root cross‐sectional area. A highly significant ploidy level (PL) main effect was found for the bluntness ratio. The lower ratios obtained for the tetraploid populations indicated that the tetraploid root tips were blunter than those of diploids, which may be a factor in soil penetration and root proliferation. The results indicated that substantial genetic variation for seedling growth characters was present among genetic backgrounds as well as within populations at both ploidy levels over a wide temperature range. It was concluded that selection for diploid as well as tetraploid rye populations possessing superior seedling growth characters over a broad range of temperatures would be successful.