الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
 |  | from | 158 |  |  |
| | | from | 158 | | |
Abstract
SUMMARY
Drought is the most important factor limiting crop productivity around the world. Hence, there are increased demands for drought tolerant genotypes as water resources and funds become limited, therefore numerous plant breeders have focused on improving genotypes of drought tolerance through understanding the effects of morphological, physiological and biochemical mechanisms on plant processes under drought stress conditions. Due to the complexity of drought tolerance, a quick and effective screen for this trait has not yet to be established. So, we need to find efficient screening method able to screen large amounts of plant material in the shortest time possible and select the most efficient genotypes.
The six parents (two exotic varieties belong to Gossypium hirsutum L., namely; Deltapine and Tamcot Camd E. and four local Egyptian cultivars namely; Giza 80, Giza 86, Giza 90, Giza 90 x Australian belong to G. barbadense L.) were crossed in all possible combinations, excluding reciprocals in 2012 growing season at the farm of Fac., Agric., Ain-Shams univerisity, Shoubra El-Kheima, Qalyubia governorate, Egypt. to obtain a total of 15 F1 hybrids. In 2013 growing season, the six parents and their 15 F1’s (21 genotypes) were planted on 2nd of April and evaluated for drought tolerance in sandy soil conditions in a private farm at Shebin El-Kanater, Qalyubia governorate, Egypt.
An objective of this investigation was to study the possibility of use morphological and physiological traits, enzymatic and non enzymatic antioxidant systems to screen large amounts of plant material in the shortest time possible under drought condition compared with the traditional selection criteria (yield and its components) used in this respect; Second objective was to study genetic analysis of yield, yield component, and fiber properties, and to determine the coefficient of correlation and path analysis between morphological, physiological, biochemical and yield to identify the more important selection indices for screening plant material to drought tolerance.
The obtained results can be summarized as follows:
First; field experimental results:
1. The results indicated that mean squares due to water treatments;100 % ETc, 1269 mm/season which represents normal water irrigation and 60 % ETc, 761 mm/season which represents drought stress, for genotypes (parents and their crosses) for all Growth traits (plant height, total fresh weight (gm) and total dry weight) and yield earliness traits (Position of first sympodial node, number of fruiting branches, days to first flower, days to first opened boll), yield and its attributes (total bolls weight (gm), number of total bolls, number of sound open bolls, seed cotton yield/plant (gm), lint cotton yield/plant (gm), lint percentage and seed index) and fiber quality properties (fiber length, uniformity index, fiber strength and micronaire reading) were highly significant revealing the presence of sufficient genetic variability in the populations.
2. Water treatments over genotypes indicated that plant height, fresh and dry weight significantly decreased under drought treatment. The genotypes Giza 90, Giza 80, P3xP4, P2xP4, P3xP6 and P5xP6 were low affected by drought treatment.
3. Position of first sympodial node, number of fruiting branch, days to first flower, days to first opened boll were significantly affected by different amount of applied water. P3xP4, P5xP6; P1xP3 and P1xP5; Tamcot C.E., Deltapine and P5xP6 showed the highest performances for yield earliness under drought.
4. Boll weight (g), number of total bolls/plant, number of sound open bolls/plant, lint percentage, seed cotton yield/plant (gm), lint cotton yield/plant (gm) and seed index significantly decreased under drought. The highest values were recorded by P3xP4, P3xP6, Giza 90 and P5xP6 for yield and its attributes.
5. Heterosis over all hybrids was highly significant for boll weight (g), number of total bolls, number of sound open bolls, seed cotton yield/plant (g), lint cotton yield/plant (g), lint percentage and seed index under the two water treatments. The highest values of mid- and better parent heterotic effects recorded for number of total bolls, number of sound open bolls, seed cotton yield/plant (g), lint cotton yield/plant (gm), lint percentage and seed index were observed by genotypes P3xP6, P3xP4 and P5xP6 under normal and drought irrigations.
6. Mean squares associated with GCA and SCA were found to be highly significant for yield and its attributes under both irrigation treatments. Combined analysis indicates that both additive and non-additive genetic effects were involved in the inheritance of these traits. The ratios of GCA/SCA were less than unity for number of total bolls and seed index under the two irrigation treatments while, the ratios for number of sound open bolls, seed cotton yield/plant (gm), lint cotton yield/plant (gm) and lint percentage differed under the two irrigation treatments. High positive and significant SCA effects were recorded by crosses P3xP4, P4xP6, and P1xP5 under normal irrigation and P2xP5, P3xP6 and P1xP6 under drought stress. Such crosses could be promising under the above mentioned environments.
7. Seed cotton yield was positively and significantly correlated with boll weight, number of total bolls, number of sound open bolls, but not correlated with lint percentage and seed index under drought treatment..
8. Concerning path analysis, number of open bolls and boll weight recorded very high order positive direct effect on seed cotton yield under normal and drought treatments. The negative direct effect on seed cotton yield was recorded by number of total boll under drought treatment.
9. Fiber quality properties, i.e. fiber length, uniformity index, fiber strength, micronaire value (fiber fineness and maturity in combination) significantly differed under normal and drought treatments. Where, the mentioned properties were low under drought than under normal treatments. Genotypes P3xP4, P3xP5, P3xP6, P4xP6, P5xP6, and P1xP4 recorded the highest values for fiber properties under drought treatment.
10. Heterosis over all hybrids was highly significant for fiber length, uniformity index, fiber strength, micronaire value under the two water treatments. The highest performance for fiber properties under stress was recorded by the genotypes P3xP6, P3xP4, P3xP5 P4xP5 and P5xP6,
11. Mean square associated with GCA and SCA was highly significant for fiber properties under both irrigation treatments. Combined analysis indicates that both additive and non-additive genetic effects were involved in the inheritance of these traits. The ratios of GCA/SCA were more than unity (predominance of additive gene effect) for fiber length, fiber strength and micronaire value under normal irrigation treatment, but uniformity index was less than unity (predominance of non additive gene effect) under drought treatment.
12. Drought indices correlation analyses revealed that stress yield was positively and significantly correlated with yield stability index and yield index and negatively and significantly correlated with stress susceptibility index. Thus, high values of yield stability index, stress tolerance index, yield index, mean productivity and geometric mean productivity and lower values of stress tolerance and stress susceptibility index suggest high drought tolerance and therefore, such indices could be used as screening criteria under drought treatment.
13. Higher estimates of heritability were found for boll weight (g), fiber length (cm) and micronair reading under normal treatment and lint %, number of open bolls, seed cotton per plant, lint yield per plant under drought treatment.
Second; Morphological, Physiological traits and non-enzymatic and enzymatic antioxidant systems as screening criteria for drought tolerance:
14. High significant differences were recorded among studied genotypes in morphological traits (root length, shoot length and root/shoot ratio), physiological traits (relative water content %, electrolyte leakage %, membrane stability index, chlorophyll ’a’, chlorophyll ’b’, total chlorophyll, chlorophyll a/b ratio and chlorophyll stability index), non-enzymatic antioxidant systems (Phenolic content, lipid peroxidation and proline) and enzymatic antioxidant systems (superoxide dismutase, catalase, ascorbate peroxidase, peroxidase activities ) under the two different amounts of water.
15. Root length increased and shoots length decreased under drought treatment and the genotypes P5xP6, P3xP4 and P1xP6 recorded the longest roots and shoots under drought treatment.
16. Root /shoot ratio increased continuously and consistently by decreasing water treatment and the genotypes Tamcot C.E., Deltapine and P2xP6 gave the highest ratio
17. Seed cotton yield per plant was positively and significantly correlated with root length (cm) while, shoot length (cm) was negatively and significantly correlated under drought and not under normal treatment.
18. Significant reduction was observed in leaf relative water content for all the genotypes under drought stress. The highest relative water content was maintained by P3xP4, P1xP5 then P1xP4 and P5xP6 under drought.
19. Drought treatment caused significant increment in electrolyte leakage % of the leaves and P3xP4, P1xP5, P1xP4, Giza 86 and P5xP6 recorded the lowest values of electrolyte leakage % under drought stress.
20. Considerable genotypic variation for cell membrane stability index was presented among the cotton genotypes. The highest values of membrane stability index % were recorded by the genotypes P3xP4, P1xP5, P5xP6 and Tamcot C.E. under drought treatment.
21. Chlorophyll ’a’, ’b’, total chlorophyll, chlorophyll a/b ratio and chlorophyll stability index (CSI %) significantly differed among genotypes under both treatments. Highest content under drought were recorded by P5xP6 followed by Tamcot C.E. and P3xP4 for chlorophyll ’a’ ; P3xP4 followed by P1xP3 for chlorophyll ’b’; P5xP6 followed by P3xP4 and Tamcot C.E. for total chlorophyll and Giza 90xAustralian, Giza 86 and Deltapine for chlorophyll a/b ratio and the highest value of CSI % was recorded by P3xP5, P1xP3, Tamcot C.E. and P5xP6.
22. Under drought treatment, it’s found that yield was positively and significantly correlated with total chlorophyll, chlorophyll ‘b’, chlorophyll ‘a’, membrane stability index and relative water content% and negatively correlated with electrolyte leakage %.
23. Drought stress caused significant increase in phenols content in comparison with normal treatment. Under the drought stress, P5xP6, Giza 90 followed by P1xP5 recorded the highest level of phenolic content suggesting that these genotypes are drought tolerant.
24. Drought significantly increased lipid peroxidation of cotton genotypes leaves in comparison with normal water treatment which had maintained low content of lipid peroxidation. The lowest lipid peroxidation content was recorded by the genotypes P5xP6, P3xP4 and Giza 80 suggesting that these genotypes are more tolerant under drought treatment.
25. Water deficit significantly increased proline content of leaves in comparison with normal water. The highest values of proline content were recorded by P3xP4 followed by P5xP6 and P2xP3 under drought stress. Such high proline content indicates drought tolerance.
26. Drought stress significantly increases superoxide dismutase, catalase, peroxidase and ascorbate peroxidase in comparison to those well irrigated genotypes. The highest activities were recorded by P5xP6 followed by P3xP4 and P3xP5 for SOD; P3xP4 followed by P1xP3, P5xP6 and P4xP5 for CAT; Giza 90 followed by P3xP4, Giza 80 and P5xP6 for POD; and Giza 90, P5xP6 followed by P3xP4 and P3xP5 for APX under drought treatment.
27. The correlation analyses revealed that yield was positively and significantly correlated with all studied antioxidants except lipid peroxidation (which was negatively and significantly correlated) under drought treatment.
In conclusion, some cotton genotypes (such as Giza 80, Giza 90, Giza 90 x Giza 90 Australian, P3xP4, P5xP6 and P3xP5) showed notable drought tolerance as measured by the common or conventional indices such as yield and its attributes, drought tolerance indices (stress susceptibility, stress tolerance index, tolerance index, yield index, yield stability index, mean productivity and geometric mean productivity). Meantime, the same above mentioned genotypes have also proved to be drought tolerant as measured by studied morphological, physiological traits and enzymatic and non-enzymatic antioxidant systems which were significantly correlated with yield. Therefore, morphological, physiological traits and enzymatic and non-enzymatic antioxidant systems could be used as effective selection criteria for screening cotton genotypes for drought tolerance especially if the breeder has large genetic pool in the shortest time possible.