The physiological control of F1 grass-dwarfs in Triticum aestivum L.

Abstract

1. The morphology and physiology of "grass-dwarfs" produced in the F 1 generation of crosses between certain varieties of Triticum aestivum L. are described. Several treatments were successful in inducing these tufted grasslike plants to flower and set seed. This enabled the crosses producing grass-dwarfs in the F 1 generation to be continued to the F 2 generation where at least half the plants possess the normal wheat phenotype. 2. The grass-dwarf phenotype in T. aestivum is probably not related physiologically to either the semi-dwarf habit or the winter habit. 3. Two main physiological groups were identified among the F 1 grass-dwarfs from different crosses. 4. The best method of producing seed from grass-dwarfs is to grow them during the early summer months under greenhouse conditions and to treat them with GA s at a concentration of 100 p.p.m, at 7-or 14-day intervals. Direct sunlight and high day temperatures enhance growth and reproductive development as does a supplement of high intensity incandescent light in the middle of the dark period. 2 5. The physiological control of flowering in normal T. aestivum and the possible roles of temperature, daylength and GA s in inducing reproductive development in grass dwarfs are discussed.

The Control of Growth Habit of Marquillo × Kenya Farmer Wheat Dwarf I by Temperature

“…The effects of the 160 temperature on the plants were 2- The reproductive responses to the temperature have been discussed previously (12). In MqlxKF 1, the high minimum leaf number for heading (8)(9)(10) leaves) accounts for its extreme sensitivity, since inactivation of the primary tiller at any earlier stage prevents the heading of the primary tiller. Secondary and tertiary tillers which have lower leaf number requirements j(4) were a-ble to head at a later time.…”

“…The temperature sensitivity of the MqlxKF I hybrids was demonstrated by the chanige from the normal (2), to the "grass-clump" dwarf (2,6,8,9), the late heading "grass-clump" dwarf (6,8) and the "lethal" (6,8,9) morphological forms as the 160 phase of the temperature regime was lengthened.…”

“…Attempts to induce growth and seed set by applications of known growth substances have shown only gibberellic acid treatments to have any promotive effect upon "grass-clump" dwarfs (7,9,12). However, even gibberellic acid was unable to overcome the lethality induced in MqlxKF 1 grown continuously at 160 (12).…”

Genes for reproductive isolation located on rearranged chromosomes

“…In general, reproductive barriers are controlled by complementary or duplicate genes (Sachs, 1953;Oka, 1957Oka, , 1974Tsunewaki and Kihara, 1962;Moore, 1966;Chu and Oka, 1972;Takahashi etal., 1976). It has been suggested by Dobzhansky (1951) that one of the complementary genes could be selectively neutral and the most effective isolating mechanism could be produced through complementary action of genes.…”

Hybrid grass-clump dwarfness in wheat: Physiology and genetics

“…It is obvious that normal growth of Type 1 dwarfs was achieved if the growing temperature was maintained at 26°C or higher, normal growth of Type 2 dwarfs required 21 °C or higher and normal growth of Type 3 dwarfs required 16 °C or higher. The data of MOORE (1966MOORE ( , 1969 would seem to'indicate that there were similar temperature requirements for the hybrid grass-clump dwarfs that he investigated but the data is not included in the table as his temperature treatments were combined with photoperiod and gibberellic acid treatments.…”