ROOT-GROWTH OF WHEAT GENOTYPES IN HYDROPONIC CULTURE AND IN THE GREENHOUSE UNDER DIFFERENT SOIL-MOISTURE REGIMES

Root characteristics of wheat (Triticum aestivum L.) genotypes are bel ieved to be important in tolerance to drought and flooding, yet neithe r the extent of differences in root size among modern soft red wheat c ultivars nor the degree of association between root size and drought o r flooding tolerance is known. This study was conducted to see whether genotypes differ in root size, and to see if root size is associated with tolerance to flooded soil and to drought during early vegetative growth. We found differences in root fresh weight (RFW), shoot fresh w eight (SFW), number of roots longer than 40 cm (NR), longest root leng th (LRL) and total root length (TRL) of 40 winter wheat genotypes grow n in hydroponic culture for 4 wk. Each of these parameters was positiv ely correlated with all others. Twelve genotypes with different root s izes selected from these 40 were grown in a greenhouse soil experiment for 3 wk, after which soil moisture treatments of control, flooding, and drought were imposed for a period of 21 d. Flooding did not affect SFW and number of tillers (NT), but decreased RFW. Drought drasticall y decreased all three parameters. The genotype x moisture treatment in teractions for SFW, RFW, and NT were significant. Root and shoot growt h of these genotypes in hydroponic culture were correlated to their ro ot and shoot growth under both control and flooded conditions, but not under drought. Thus, it appears that the expression of genotypic root growth potential may be influenced by the availability of soil moistu re, and that selection of wheat seedlings for vigorous growth in hydro ponic culture will select for vigorous early growth in soil with adequ ate or excess moisture, but not under severe drought.