Productivity and Survival of Alfalfa Hybrid and Inbred Plants Under Competitive Conditions1

Abstract

A study was conducted at Perugla, Italy in 1981 to evaluate the importance of intra‐specific competition in alfalfa (Medicago sativa L.) and to investigate the consequence of different percentages of inbred seeds on forage yield. Three seed mixtures having ratios of inbred seed to hybrid seed (S1/F1) of 1/9, 3/7, 1/1 were sown, seed by seed, in micro‐plots (50 ✕ 30 cm) at a seeding rate of 1600 seeds/m2. Data were collected on establishment, green matter yield per plant of inbred or hybrid origin, dry matter yield per plot at first, second, and third cut, height and number of stems per plant at the third cut, and number of plants alive in the fall season. The results are summarized as follows: 1) yield of S1 plants was much lower than that of F1 in each of the three mixtures; the inbreeding effect was higher than that usually shown in spaced plant trials; 2) since no differences were observed in dry matter yield per plot among mixtures, differences in S1 seed percentage would not seem important to productivity of alfalfa in the 1st year; and 3) no differences were observed in establishment between S1 and F1 seedlings but fall survival percentages of S1 plants were significantly lower than those of F1 in all mixtures. This confirms that selective elimination of S1 plants begins during the seeding year. The selection against S1 plants increases over time and suggests that 1 year after seeding few S1 plants will survive irrespective of their percentage in the initial seed lot.