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Sorghum Root Morphogenesis and Growth. I. Effect of Maturity Genes¹

Root development of two sorghum [Sorghum bicolor (L.) Moench.] maturity isogenic lines (early x 60 SM and late x 100 M) was closely studied in plants growing up to 38 days after emergence (DAE) in hydroponics. Each adventitious (crown) root was tagged upon appearance and periodically measured for length. Root diameters, root volume, leaf area, and transpiration were also measured periodically. Seminal roots and mesocotyls were removed on some plants at 10 DAE, in order to simulate the effect of some common fungal or insect damage in the field.

The onset of initiation of adventitious roots occurred at 4 and 6 DAE in the early and late genotypes, respectively. Root initiation rates cycled with time, within a range of 0 to 1.5 roots-plant-_l–day_–1. Cycling of root initiation rates appeared to correspond with the formation of concentric whorls of these roots in the crown. Total number of adventitious roots at 38 DAE was 17 and 23 in the late and early genotypes, respectively. In the early genotypes, growth rate of adventitious roots that were initiated at an early stage was the same as for roots initiated later, being about 3 cm day^–1 In the late genotype, growth rate of later initiated roots was slower than that of roots initiated earlier. Although the early genotype had a greater total adventitious root length per plant than the late one, the latter had a greater root volume than the former, due to greater number and growth of lateral branches.

Removal of the seminal root and mesocotyl increased the number and growth of lateral branches of existing adventitious roots and subsequently increased root volume in the early genotype. Similar effects were not observed in the late genotype.

Key Words: Sorghum bicolor (L.) Moench • Seedlings • Hydroponics • Transpiration • Breeding

² Visiting associate professor, presently at the Volcani Center, ARO POB 6, Bet Dagan, Israel; and associate professors, Texas Agric. Exp. Stn., Texas A&M Univ., Blackland Research Center, Temple, Tex.

Received for publication July 6, 1976.