EFFECT OF GAMMA RADIATION ON FIBER TECHNOLOG-ICAL CHARACTERS AND YIELD OF SOME EGYPTIAN AND UPLAND COTTON CULTIVARS

The dry seeds of the two Egyptian cotton cultivars Giza 77 (extra-long staple) and Giza 75 (long-staple), Gossypium barbadens L., and one upland cotton cultivar (McNaire 220), G. hirsutum L., were ex­posed to four Y-ray doses (0.0, 5.0, 10.0 and 15.0 Kr) emitted from Cobalt-60 to study the direct effect of Gamma rays on fiber technologi­cal characters and yield during two successive growing seasons 1990 and 1991. It was found that Giza 77 was superior than the other cultivar with respect to all fiber properties except seed cotton yield. With re­spect to Giza 75, it was intermediate in all studied characters. Whereas, McNaire 220 ranked the third in most characters except in seed cotton yield, lint percent and seed index, where it ranked flist. It was also the second in micronaire reading. The 5-Kr dose did not affect lint percent of Giza 75, fiber length at 2.5% and 50% SI of the three cultivars and micronaire reading of McNair 220. Generally, increasing the doses of y rays decreased the values of most traits studied. The highest decrease was obtained at 15-kr dose. The exceptions were; seed cotton yield and micronaire reading of the three cultivars; and fiber flat-bundle strength at zero and 1/8 inch gauge lengths of McNaire 220, where increasing the dose increased the values of these traits, a matter that needs fur­ther investigation.