The heritability of agronomic characteristics in tall fescue (Festuca arundinacea Schreb.)

Abstract

Three genotypes of tall fescue (Festuca arundinacea Schreb. cultivar Fawn and four genotypes from the cultivar Fortune were used as parents to form 15 of a possible 21 single crosses to study the heritability of certain agronomic characteristics. The Fawn variety is considered to be tall in growth habit, vigorous and early in anthesis. The Fortune variety represents germ plasm with a shorter growth habit, less vigor and later anthesis. Crossing was accomplished by mutual pollination in the greenhouse during February 1972. A greenhouse experiment was started in June 1972 using the 15 single crosses in a randomized block with three replications. Plants were supplied with one half strength of a modified Hougland's solution twice weekly until August 3 followed with an application of the same nutrient solution every two weeks until they were taken to the field for establishment. Greenhouse data were collected on July 7, August 4 and September 11. These data indicated that the variation among single crosses for tiller numbers and dry weight were greater as the plant grew older. Nutrient stress affected dry matter yield by reducing the variation and mean performance of the single crosses. Differences among single crosses for shoot length, tiller number, and plant spread were still quite evident under the stress conditions. Shoot length showed significant general combining ability (GCA) with non significant specific combining ability effects (SCA) on July 7 and September 11. GCA effects for tiller numbers were evident on August 4 and September 11. Both GCA and SCA effects were significant for plant spread on September ii. GCA for dry weight were significant only on July 7. Based on the diallel analysis, additive gene action was primarily responsible for shoot length, tiller numbers and dry weight. Both additive and non additive gene action influenced plant spread. The field establishment included the 15 single crosses from greenhouse experiments and the seven parent clones, established in a randomized block design with three replications. From the diallel analysis, it was observed that the GCA:SCA mean square for the characters measured were: plant height (19:1), plant spread (2. 1:1), anthesis date (3.2:1), panicle number (1.4:1), panicle length(l2:1), number of primary pedicels per panicle (7.4:1), five panicle seed weight (0. 2:1), seed yield per plant (0. 4:1) and 100 seed weight (15.1:1). This indicated that additive gene action was of major importance in the expression of plant height, number of primary pedicels and 100 seed weight. Non additive gene action was contributed substantially more to the expression of five panicles seed weight and seed yield. Both additive and non additive gene action contributed to plant spread and anthesis. Inferences about gene action for panicle numbers and panicle length were not as evident. This is because of the low GCA:SCA ratio, a barely significant GCA for panicle number, and no significant GCA or SCA for panicle length. Single cross progeny were superior to mid parent for plant height (9.27 percent), plant spread (20. 33 percent), anthesis (20.90 percent, which suggested earlier anthesis than mid parent), panicle number (36. 69 percent), and panicle length (11. 44 percent). No apparent superiority of single cross progeny over their corresponding mid parent for number of primary pedicels and 100 seed weight was observed. Of all single crosses, only Fawn x Fortune crosses were inferior to mid parents for five panicle seed weight (65.93 percent) and seed yield (60. 22 percent). The Fawn x Fortune performance for both of these characters (0.4062 and 1.23 g per plant, respectively)was low, The diverse parentage of these crosses may have resulted in irregular meiotic behavior in the F₁ which in turn may have caused inviable gametes to be formed. This sterility would result in the low seed yields observed. This is a problem that should be cytologically investigated. Crosses between diverse germ plasm (Fawn x Fortune crosses) did result, however, in heterosis for all characteristics except number of primary pedicels and 100 seed weight. But Fortune x Fortune crosses, for certain characters such as plant height, plant spread, panicle numbers, panicle length,exhibited even more heterosis. No heterosis was observed in the Fawn x Fawn crosses. Medium to high heritability estimates were observed for 100 seed weight, plant spread, anthesis date, panicle number and panicle length, while medium to low heritability were observed for panicle length. Low heritable value was evident for plant height, number of primary pedicels, five panicle seed weight and seed yield. Heritability estimates were based on parent progeny relationships involving all single crosses and mid parents. The relationships among various plant characteristics and seed yield was studied. Five panicle seed weight and panicle numbers were significantly correlated with seed yield. However there was a non-significant association of panicle length with seed yield and number of primary pedicels with seed yield.These relationships suggest that higher yielding genotypes may be identified by observing only few panicles per plants. The panicle characteristics examined in this study (other than seed weight) were of little value in identifying high seed yield genotypes, but panicle seed weight was positively related to plant yield.