INVESTIGATIONS OF THE ENVIRONMENTAL AND GENETIC FACTORS AFFECTING EARLINES3 IN COTTON, GQSSYPIUM HIRSUTUM L.

INVESTIGATIONS OF THE ENVIRONMENTAL AND GENETIC FACTORS AFFECTING EARLINES3 IN COTTON, GQSSYPIUM HIRSUTUM L.

Abstract:

Agronomic and genetic aspects of early maturity in cotton were investigated using seven varieties of cotton originating from diverse backgrounds. The varieties used are: 2421 – K.4489 (V ), Striper 61-15: 62-7 (V2), Arkansas 52-21 (V3), Samaru 71 (V.), Samaru 72 (V5), Samaru 26J (V6) 3 ‘ 4 1 5 , 6 and UK66 (V7). The agronomic trials were conducted in 1975 and 1977. Three sowing dates and three levels of nitrogen were employed in 1975 whereas three sowing dates and two nitrogen levels were used in 1977. In the genetic trials, two series of experiments were conducted in 1976 and in 1977. Firstly, a diallel cross series involving all the seven varieties, their F1’s, and F2 ‘s were put into trials under two contrasting conditions of June and July plantings in each year. Secondly, a series of selected specific crosses involving parents of different maturity dates, their F1 ‘s, F2 ‘s and backcrosses were tried under June sown conditions only in the two years. In each case, observations were made on several earliness and yield characters. When the two-year results of the agronomic trials were combined, none of the characters was influenced by planting dates or nitrogen levels. There were, however, significant interactions between the year and each of these two main factors for days to first flower (DFF), and between the year and the dates for seed weight and number of seed. In this respect, both the node of the first fruiting branch (NFB) and DFF can be regarded as reliable measures of earliness. The individual analyses showed that early sowing date had favourable influence on most of the earliness and yield characters in both years, while higher nitrogen levels favourably influenced yield and related characters more than those of earliness in 1975. Combined first and second picks as a percentage of the total pick (E2%) was also found to be a good measure of earliness as it showed a most distinguishing effect between the early and the late types. However, there was a considerable change of ranking between the early and the intermediate varieties for various characters. Nevertheless, V and V were consistently early maturing. In the diallel studies, there was no significant difference in maturity between crop sown in June and that sown in July, but on the average, the 1976 crop took longer to mature than the 1977 crop. The general combining ability (gca) mean squares were very large while the specific combining ability (sea) mean squares were very small (or even zero) for all characters in both the F and the F analyses. This would seem to indicate that the varieties were heterogeneous and probaly heterozygous also. F1 hybrids of early maturing parents were found to be earlier than hybrids of late maturing parents, and some of the hybrids, especially those involving V1 V2 and possibly V , combined earliness with high productivity. Positive and negative gca effects for the different characters also indicate that some of the varieties had combinations of characters favourable for the expression of earliness. Hence their initial improvement through breeding seemed promising. The significant year x gca and year x sea interaction would necessitate measuring these effects over years. When the two planting conditions were considered separately, it was noticed that NFB and DFF were reliable measures of earliness for the June planting and E2% for the July planting conditions. In the specific cross studies, there was an indication of dominance for earliness in both the early x late and the early x intermediate crosses, but the nature of the variances would not permit a reliable estimation of the genetic parameters. There were a few cases of heterotic effect when measured as the difference between the F1 and the mid-parent value, but in general heterosis was not frequent in these studies. In addition, the total number of sympodial branches on the main stem (MSB) per meter of plant height was also measured. Considering this as some measure of relative productivity, it was noticed that, the early maturing varieties had higher NSB/meter of PHT than the late ones, despite the fact that the former wore shorter plants and had fewer NSB. Narrow sense heritability (h2) estimates showed high values for most earliness characters in both the early x late and the early x intermediate crosses, thus indicating that these characters would respond favourably to selections. In the genetic studies, it was generally noticed that the variances of the non-segregating generations were larger than those of the segregating generations for some characters. This was largely due to the bulking of selfed seed from different rent individual plants which presumably increased the variability of the parental generation. Nevertheless, it is possible to breed for earliness in these varieties at least initially without the complications of dominance and epistasis.

INVESTIGATIONS OF THE ENVIRONMENTAL AND GENETIC FACTORS AFFECTING EARLINES3 IN COTTON, GQSSYPIUM HIRSUTUM L.

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