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.
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Date
1979-07
Authors
Mustafa, Shettima
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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.
Description
A Thesis
Submitted to the Faculty of Agriculture,
Ahmadu Bello University Zaria,
In Partial Fulfilment of the Requirements
for the Degree
of
Doctor of Philosophy
by V
Shettima Mustafa
JULY 1979
Keywords
INVESTIGATIONS,, ENVIRONMENTAL,, GENETIC,, AFFECTING EARLINESE,, GQSSYPIUM HIRSUTUM L.