Characterization of Elite Upland Cotton Genotypes for Earliness and Yield Traits

Short duration cotton genotypes increased the chances to harvest crop before cold and rainy weather conditions. However, earliness in cotton is a difficult character, which is assessed by determining many plant traits. The current experimental was conducted at Cotton Section, A.R.I. Tando Jam, during kharif season 2013. The eight cotton genotypes including CRIS-342, Sindh-I, Haridost, Malmal, Bt-121, Bt-3701, TS-501 and Shahbaz were sown in randomized complete block design with four replications. In a total, seven quantitative traits were measured such as days to first flowering, node number to set first sympodial branch, node number to set first flowering, sympodial branch length (cm), sympodial branches plant, number of bolls plant, seed cotton yield plant (g). The mean squares from analysis of variances showed that genotypes differed significant (P≤0.01) for all the studied traits, demonstrating a vast genetic variability in tested genotypes. The genotypes, Sindh-1, CRIS-342, Bt-121 and Bt-3701 were characterized as early maturing or short duration cotton varieties. However, the correlation between yield and earliness traits were best criteria for developing the short duration cotton yield varieties.


INTRODUCTION
Cotton (Gossypium hirsutum L.) is an important fiber crop in the world.Its seed is used as raw material in oil and forage industries due to the high percentage of the oil and protein [1].Early maturing varieties increase the possibility that harvest can be completed before cold and rainy weather.Earliness in cotton is a complex character which is assessed by measuring many plant traits.The traits like node of first fruiting branch, 1 st sympodial branch node number on main stem, date of 1 st flower and date of 1 st open boll are used for assessing earliness in cotton [2].It is very important in alleviating late season risks of insects/pests (particularly bollworms), diseases, unfavorable weather conditions and increase in economic return by reducing input cost [3].Another advantage of growing early maturing cotton cultivars is the provision of proper time for rotation of other crops, allowing timely sowing of wheat in cotton-wheat-cotton cropping system as in Pakistan [4].The early maturing varieties require lesser inputs i.e. use of fertilizer, fewer sprays, irrigation and escape late season pest attack and avoid soil moisture depletion and weathering of open cotton [5].Due to these reasons, breeding for early maturing cotton varieties has become an important task in cotton breeding.Therefore, the current research was designed to identify selection *Address correspondence to this author at the Agriculture Research Institute Tandojam, Tandojam, Pakistan; Tel: 0223405288; E-mail: dr_shahnaz_memon@yahoo.com criteria for the development of early maturing cotton genotypes.

MATERIALS AND METHODS
The present study was conducted in the experimental area of Cotton Section, Agriculture Research Institute.Tando Jam, during 2013.The experimental materials comprised of eight cotton genotypes such as CRIS-342, Sindh-1, Haridost, Malmal, Bt-121, Bt-3701, TS-501 and Shahbaz, which were sown in randomized complete block design with four replications.The row to row and plant to plant space was maintained at 75 and 30 cm, respectively.All the agronomic and cultural practices were performed regularly from sowing till to harvest.Twenty plants were chosen to record the data on days to 1 , number of bolls plant -1 , seed cotton yield plant -1 (g).After taking the raw data from field, the secondary data were analyzed in computer package Statistix 8.1 version to determine analysis of variance and correlation between earliness and yield traits while graphs were draw in MS-excel.

Mean Performance
The mean squares from analysis of variance (Table 1) showed that all the traits for earliness and yield traits were significant (P≤0.01)among the evaluated genetic resources, demonstrating that varieties performed differently for the character and these traits are best indicators for developing early maturing cotton varieties with optimum seed cotton yield.Similar results were obtained by [2,3] they also observed significant differences for the earliness and yield traits.
The data regarding the mean performance for all the quantitative traits were presented in Table 2 and Figures 1 and 2. Number of days taken to flowering is considered as an important determinant of earliness [4].It is normally assumed that fewer the number of days taken to produce first flower, the earliest is the boll setting and opening; hence earlier the variety.Among the eight cotton genotypes, the Sindh-1 recorded minimum (39.00days) days to first flowering, followed by Bt-121 (40.00 days), whereas TS-501 exhibited maximum (4.00 days) for first flowering, because delay in flowering is the sign of late maturity and susceptible to heat.Similar results were obtained by [6,7] who found positive linkage between first flower  and earliness and showed that additive gene effects controlled days to flowering.
Node number can be determined early in the season, it can be easily and precisely identified and it is in-dependent of complications arising from shedding of fruit forms.When considered in terms of rate of fruit development and maturity, earliness may be defined.Sindh-1 had the lowest value of 5.00, followed by Bt-3701 with respective value of 6.25 to set node number first sympodial branch, while Shahbaz set first sympodial branch at higher (9.25) node.Several other workers [3,8] have also reported strong relationship between lower sympodial branch node number and early maturity in cotton.
Flowering setting at base of the plant or minimum node number shows early maturity and also tolerance to high temperature.Setting-up of first effective boll on lower sympodial branches can also be regarded as one of the criterion for early maturing varieties.The lowest value of 4.25 was exhibited by Sindh-1, followed by  Shahbaz (5.50), and the highest by Haridost with a value of 9.75 (Table 2).Strong relationships between early maturity and lower sympodial branch node number with effective boll have been reported by several other cotton breeders [3].It is also assumed that, closer the distance between the first sympodial branch node and first effective boll setting branch, the earlier the variety would be [9].
The varieties also differed significantly (P≤0.01) for sympodial branch (fruiting branch) length that varied from a minimum length of 8.75 cm to a maximum of 25.00 cm (Table 2).Short sympodial branches are desirable for early maturing varieties, Bt-121 characterized short (8.75 cm) sympodial branch length and Bt-3701 was next scoring which measured (9.50cm) sympodial branch length.However, Haridost measured long (25.00cm) sympodial branch length.Cotton breeders have been succeeded in developing early maturing varieties with short sympodial branches.Some other workers [3,10] also rated varieties with short sympodial branches as early maturing ones.

Sympodial branches plant
-1 tends to have direct relationship with bolls plant -1 and seed cotton yield.
Sympodial, the fruiting branches has important role in managing yield through bolls plant -1 .Sympodial branches which set the maximum number of bolls plant -1 , more sympodial branches plant -1 cannot be sure for maximum boll setting plant -1 because it depends upon mode of boll bearing and shading.The genotypes CRIS-342 and Malmal both showed minimum and same value of 19.25, followed by Sindh-1 (21.25) however, TS-501 recorded maximum (29.25) sympodial branch plant -1 .Many research workers like [9,11] who also observed similar findings.
Boll number plant ; whereas Sindh-1 set the maximum (77.25) number of bolls plant -1 in cotton plant.In the accordance of many researcher of [12,3] who reported that early maturing cottons although had comparatively smaller or moderate bolls but produced better yields, may be due to setting and picking more number of bolls at early stages of boll opening, as compared to late maturing cottons.
Yield is a complex polygenically inherited character, resulting from multiplicative interaction of its contributing characters.It is highly influenced by the environment; hence selection based on yield alone may limit the improvement.Whereas the component characters of yield are less complex in inheritance and are influenced by the environment to a lesser extent.Thus, effective improvement in yield may be brought about through selection for yield component characters.The highest seed cotton yield was obtained CRIS-342 (256.93g),followed by the Sindh-1 of 247.15g and the lowest seed cotton yield produced by the parent Haridost of 163.30g.Similar results were also obtained by [9,5,13] who also recorded optimum yield with early maturing genotypes.

Correlation between Earliness and Yield Traits
The correlation coefficient between earliness and yield traits is presented in Table 3 which exhibited that days to initial flowering had significant positive associated with node number to set first flowering (r = 0.55**), node number to set first sympodial branch (r = 0.77**), sympodial branch length (r = 0.65**) and sympodial branches plant -1 (r = 0.58**); nevertheless days to initial flowering made significant but negative correlation with number of bolls plant -1 (r = -0.46*)and seed cotton yield plant -1 (r = -0.41*).The negative correlation revealed that heat susceptible genotypes reduced the number of bolls plant -1 and seed cotton yield due to high temperature.If negative association between characters is due to pleiotropic effects it would be very difficult to obtain the desired combinations, while if linkage is involved, special breeding programmes are needed to break these linkage blocks.
Node number to set first sympodial branch were positively correlated with sympodial branch length (r = 0.35*) and sympodial branch plant .
Sympodial branches plant -1 was positively but nonsignificantly correlated with of bolls plant -1 (r = 0.10) and negatively but also non-significantly with seed cotton yield (r = -0.07).It corroborates with the results of [5,13] they reported positive and significant correlations were estimated between yield and earliness characters.
Yield component characters show association among themselves and also with yield.associations between desirable attributes will help improvement a joint manner.Whereas, unfavorable associations between the desirable attributes under selection may limit genetic advance.Hence, knowledge of associations between the yield components and also among themselves is essential for planning a sound breeding programme.However, number of bolls plant towards seed yield has also been reported by [14,15,16,17].Therefore this trait appears to be most important in influencing seed cotton yield in cotton and selection should be oriented towards high boll number.

CONCLUSION
Among the cultivars, Sindh-1, CRIS-342, Bt-121 and Bt-3701 were characterized as early maturing or short duration cotton varieties.However, the correlation between yield and earliness traits was best criteria for developing the short duration cotton yield varieties.

Figure 1 :
Figure 1: Mean performance of cotton genotypes for days to first flowering, node number to sett first sympodial branch, node number to set first flower and sympodial branch length (cm) for earliness.

Figure 2 :
Figure 2: Mean performance of cotton genotypes for sympodial branches plant -1 , number of bolls plant -1 and seed cotton yield plant -1 (g) for earliness.

- 1 ( 1 and seed cotton yield plant - 1
r = 0.62**) and significantly and negatively associated with number of bolls plant -1 (r = -0.56*)and seed cotton yield plant -1 (r =-0.64**).It is suggested that due to high temperature bolls shading were taken place; thus number of bolls plant -1 and seed cotton yield plant -1 was negatively associated with node number to set first sympodial branch.Sympodial branch length was significantly but negatively correlated with number of bolls plant -1 (r = -0.62**)and seed cotton yield plant -1 (r = -0.64**),which exhibited that increase in sympodial branch length, will cause a significant decrease in number of bolls plant -

Table 1 : Mean Squares from Analysis of Variance for Earliness and Yield Traits Upland Cotton Genotypes
**Significant at 1% probability level.