INHERITANCE OF THE MULTIFOLIOLATE TRAIT IN TETRAPLOID ALFALFA, MEDICAGO SATIVA L.

Abstract

Inheritance of the multifoliolate leaf (MFL) characteristic (leaves containing more than three leaflets) in tetraploid alfalfa was studied. Also, the effects of temperature and short-term aging of a few weeks on the expression of the MFL trait were determined. Broad sense heritability of the trait was also estimated. Two sets of diallel reciprocal crosses were intially made in the greenhouse using vacuum pump and alcohol for emasculation of the seed parent. There were six different clones in each set. Set I contained ML₁, ML₂ ML₄₉, ML(G), Lew-1, and Hayden-1 clones. The average number of leaflets per leaf for the above mentioned clones was 5.65, 4.52, 3.55, 3.20, 3.00, and 3.00, respectively. Set II was composed of ML₇, ML(F), ML₁₂, ML₅₂, N₁, and N₂ clones with the average number of 4.75, 4.15, 3.50, 3.25, 3.00 and 3.00 leaflets per leaf. Based on the F₁ and S₁ progenies, it was hypothesized that at least three major and independent genes, each with equal contribution to the expression of the MFL trait, were involved. This hypothesis was later substantiated by the observed segregation ratios of the 75 F₂ families from the cross Lew-1 x ML₁ which closely fit the expected ratios. These three genes, LA, LB, and LM showed incomplete dominance with additive gene action. No evidence for epistasis was found. There was a positive association between the number of dominant alleles and the degree of expression of the MFL trait. This association was so specific that plants with less than four, four, five, six, seven or more dominant alleles had an average number of 3.0, 3.1, 3.2-3.4, 3.5-4.0, and 4.1 or more leaflets per leaf respectively. Analysis of the 11 reciprocal crosses between trifoliolate (TFL) and MFL clones showed that only two reciprocal crosses produced a significantly higher number of MFL than TFL plants when the female parent was a MFL clone. Maternal or cytoplasmic effects were negligible. The average frequency of MFL leaves of the two clones (ML(G), ML₂) studied did not significantly change under warm (34°C, 25°C) and cool (17°C, 15°C) temperatures. There was no significant change in the expression of the MFL leaf frequency trait in these two clones from the first harvest scoring to the next. Plants were scored before harvesting at full bloom. Calculated broad sense heritability of the MFL trait was 86%. This indicates that the recurrent selection method for several cycles should increase the frequency of MFL plants in an alfalfa population very rapidly. There are excellent opportunities for improving the quality of commercially grown alfalfa by incorporating the MFL trait.