Genotypic response of South African wheat cultivars to photoperiod, vernalization and adaptation

English: The aim of this study was to determine the response of South African bread wheat cultivars to vernalisation and photoperiod and to group the genotypes accordingly. In addition to this the way in which the response of genotypes to vernalisation and photoperiod attributes to yield stability was also investigated. Thirty South African wheat cultivars were included in two separate trials to evaluate their response to vernalisation and photoperiod treatments. The wheat cultivars were selected to represent cultivars planted in all the main wheat production regions of South Africa. The range of genotypes included cultivars with no vernalisation requirement to cultivars with very strong vernalisation requirements. The vernalisation trial consisted of 30 South African wheat cultivars subjected to eight vernalisation treatments, ranging from zero to seven weeks vernalisation. Each treatment had eight replicates on which days to heading, flowering and physiological maturity were observed. Cluster analysis was done to group the cultivars into similarity groups. Four groups were identified: 1) True winter wheats encompassing: Molen, - - SST936, SST966, SST399, and 2) Winter wheats that included Betta-ON, Caledon, Elands, Hugenoot, PAN3235, SST367, and SST983, 3) Intermediate wheats consisting of Gariep, Limpopo, PAN3211, PAN3349, PAN3377, SST124, SST363, and Tugela-ON, and 4) Spring wheats including Baviaans, Inia, Kariega, Marico, Palmiet, Steenbras, SST57, SST65, SST88, SST822, and SST876. The photoperiod trial involved 30 South African wheat cultivars subjected to three photoperiod treatments (10, 14, and 18 hours day light). Ten replicates were included for each treatment. Days to heading, flowering and physiological maturity were recorded for all cultivars. Cluster analysis was performed and four discreet response classes identified. The classes were denominated as Group 1, Group 2, Group 3, and Group 4. Group 1 consisted of only one cultivar SST399. Group 2 included all the following true winter, winter, and intermediate wheat cultivars: Molen, Betta-DN, Caledon, Elands, Hugenoot, PAN3235, SST367, Limpopo, Gariep, PAN3211, PAN3349, PAN3377, SST124, SST363, and Tugela- ON. The only cultivars in Group 3 are the hybrid wheats: SST936, SST966, and SST983. Group 4 included all the spring wheat cultivars: Baviaans, Inia, Kariega, Marico, Palmiet, Steenbras, SST57, SST65, SST88, SST822, and SST876. Data obtained from the vernalisation and photoperiod trials were used in conjunctiqn with data from cultivar evaluation trials to determine the relationship between the response to vernalisation, photoperiod and yield stability. Yield data from the three main wheat production areas: Free State (14 sites), Irrigation areas (13 sites), and the Western Cape (12 sites) were used to calculate yield stability. Correlations between response to vernalisation, photoperiodic and yield stability were found to be weak, although stronger correlations were observed between vernalisation response and yield stability in the Western Free State, Central Free State, and warmer irrigation areas. The data from this study suggest that wheat should be classes as true· winter, winter, intermediate, and spring wheats, and that trial layouts should be planned according to these classes.