The effect of temperature on radiation-induced macromutants of Arachis Hypogaea L. and expression of heterosis in F1 hybrid populations

Three separate experiments were conducted with cultivated peanuts to (a) study the effect of four controlled temperatures on the expression of seven radiation-induced macromutants and the mother line; (b) determine the responses of normal appearing F₁ hybrids involving four macromutants to three controlled temperature regimes and (c) evaluate the same macromutant, parental and F₁ hybrid populations (described in b) when grown for a full season under field conditions.

Macromutant plant weights and flower production were generally lower than that of the mother line in all three experiments. The macromutants also tended to flower later than the mother line. The leaflet expression of two of the macromutants was drastically influenced by changes in temperature. Lupinus reached maximum leaflet curvature when grown at 34/30°C but appeared near normal when grown at 22/18°C. The reverse was true for the macromutant Recurved. The macromutant Flop contained maximum percentages of nitrogen and phosphorus in its vegetative parts when grown at the highest temperature (34/30°C). All other mutants and the mother line had highest proportions of these nutrients when grown at the lowest temperature regime (22/18°C).

Expressions of heterosis were maximized when hybrids of macromutant parentage were grown at suboptimal temperatures. General combining ability estimates were higher than specific combining ability estimates with the macromutant Hedera (a dwarf type) making the greatest contribution to the general combining ability effects for peg (fruit-bearing structure) production and pegging efficiency. The same macromutant was found to make substantial contributions to general combining ability effects for fruit and seed weight when hybrids were grown under field conditions.