Tolerance of Egyptian Cotton Varieties (G. barbadense L.) to Late Planting

This study was done to evaluate two sets of Egyptian cotton varieties (G. barbadense L.) for tolerance to late planting. The first set included 16 cultivated and obsolete varieties which evaluated for two seasons under early and late plantings. The second set included eight varieties selected from the first set for tolerance to late planting; four susceptible and four tolerant, and evaluated for three seasons. In the first set, mean squares of all the studied traits indicated significant (p ≤ 0.01) differences among varieties in separate and combined analyses under early and late plantings. Also, the combined analysis showed significant (p ≤ 0.01) differences between dates for all traits.  However, the interactions of varieties × dates and varieties × dates × years were not significant. The mean square of varieties × years was significant only for lint percentage, boll weight and days of first flowers. Furthermore, the interaction mean squares of varieties x years under both of early and late planting was not significant indicating that the different traits were stable from year to year either for early or late planting. Late planting caused severe reduction in seed cotton yield reached 19.28, 19.14 and 19.21 % in the first, second year and combined date. Stress susceptibility index varied slightly from year to year. The highest stress susceptibility index was recorded for the varieties Giza 81 and Menoufi (1.19) followed by Giza 85 (1.20), Giza 88(1.20), Giza 69 (1.15), Giza 95 (1.15), Ashmouni (1.10) and Giza 92 (1.04). The highest yielding varieties (G90× Aus, Giza 90, Dandara, Giza 86 and Giza 80 were tolerant to late planting and scored stress susceptibility index less than unity. The highest varieties in lint yield were G90× Aus, followed by Giza 90, Giza 80, Giza 86 and Giza 95 under both planting dates. The reduction % in lint yield caused by late planting was very high and larger than that in seed cotton yield, and reached 22.88, 22.56 and 22.72 in the first, second year and combined data, respectively. The stress susceptibility index of the different varieties respect lint yield / plant showed the same picture as seed cotton yield /plant. The reduction in lint% for different varieties was low and averaged 4.53, 4.41 and 4.47 % in the first, second season and combined means, respectively. The reduction % in boll weight caused by delaying planting data was high and reached 21.79, 20.85 with an average of 21.31 %. The reduction% in boll weight was more than that in seed cotton yield. Therefore, number of bolls /plant increased under late planting. These results indicate that the stress of delay planting shortened the vegetative period of cotton growth. The results of the second set of varieties were in the same trend of the first one. These results indicate that the main cause of reduction in cotton yield is late planting date. This is due to that all the Egyptian cottons were bred to grow under full season and not for short season conditions. However, the stress susceptibility index indicated to the presence of tolerant varieties to late planting, and there is a chance to select for short season condition from the progenies of the crosses of such tolerant varieties.