Performance of Diallel Crosses and Second Generation Synthetics of Alfalfa Derived from Partly Inbred Parents. II. Earlines and Mortality¹

Abstract

In an alfalfa (Medicago sativa L.) breeding study conducted under conditions of high competition between plants, combining ability for earliness and mortality was evaluated from diallel crosses among selected parents, which had been partly inbred by selfing. The performance of first and second generation synthetics was also studied. For both earliness and mortality (percentage of blooming or dead plants, respectively), general combining ability (GCA) was considerably larger than specific combining ability (SCA) for all generations of parental inbreeding (S0, S1, S2, S3, and S4). GCA and SCA increased with the level of inbreeding. Significant correlations were noted between earliness and yield, between mortality and yield and between earliness and persistence. At each level of parental inbreeding the single crosses with the greatest forage yield were also the earliest and the most persistent. Syn 2 generation synthetics had the same response pattern.

Seed and forage yield of advanced generation synthetics of berseem clover derived from partly inbred parents under different harvesting regimes

“…The only comparison of selfing generations for synthetic varieties of forage crops that has encompassed as many generations as the present study (from S 0 through to S 4 ) was reported by Rotili (1976) for forage yield of alfalfa. As a function of selfing generation, a curvilinear pattern of response also emerged in this study of Rotili (1976), which featured a plateau in the S 2 generation. Later on, Rotili et al.…”

“…Studies of forage crops have not provided definite evidence for the usefulness of inbreeding in selection schemes (e.g. Rotili 1976, Berdhal and Ray 2004). In berseem populations, self‐fertility decreases dramatically with increased inbreeding, although many plants with high self‐fertility can be located within populations (Iannucci 2001a).…”