General Commission for Scientific Agricultural Research-
Hassakeh Research Center
Aleppo University, Faculty of Agriculture
Cotton is ranked firstly among lintel crops because of its economic importance and wide planted areas in the world. In Syria, cotton is an important crop among irrigated crops. It is mainly planted in Hassakeh which comes firstly in production and planted area, followed by Raqqa, Aleppo, Deir Ezzor, al-Ghab, Edleb, Hama and Homs.
As a result of the expansion in cotton planted area, many difficulties appeared such as:
diseases, insects, physiological problems in addition to buds and unripe bolls shedding which comes firstly in the problems that affect cotton production in Syria. This phenomenon is caused by many factors, but high temperature is the most important mean of shedding in cotton. The high temperature in July and August which associated with flowering and fruiting periods in cotton causes a large reduction in remained bolls on plant and lint yield. Therefore, breeding programs for improving heat tolerance in cotton is an insistent necessity under high temperature condition.
The research aimed to: Obtain heat tolerance hybrids, determine combining ability in the parents, and select best parent(s) have heat tolerance character and best hybrid(s) could be used in breeding programs for this.
The research was carried out in three seasons 2005, 2006 and 2007. In the first season (2005) ten parents of cotton Gossypium hirsutum L. : Aleppo 90, Aleppo 118, Raqa 5, Deir Ezzor 22, Tashqend 6, CIM 70, DP 41, DP 70, Stonvill (BR 115) and Stonvill (BR 636) were planted in the research station of cotton at Tel-Temr\ Al-Heseke , on two rows (5m) length. At flowering stage diallel cross were done, and some flowers of each parent were selfied by banding it to keep its genetic pureness.
In the second season (2006) the parents and hybrids were planted in Tel-Temr\Hassakeh two rows (5m) for each entry, using Randomize Complete Block Design. Some flowers of each parent were obliged to self pollinated to get F2. Some earliness parameters, productivity and technological characters were assessed.
In the third season (2007) the parents, hybrids and F1 were planted in two locations: Tel-Temr\Hassakeh and Al-Mreiyah/Deir Ezzor by the same way. Some productivity characteristics and shedding rate were studied.
Germination rate of pollen tube of parents and (F1) was studied in laboratory, at different levels of temperature: 25-28-30-32-35-38 C for 24h to estimate heat tolerance in parents and hybrids.
Data were analyzed using a statistic program Genstat 7, and Heterosis, General Combining Ability (GCA), Specific Combining Ability (SCA), Heritability and shedding rate were estimated.
The Heterosis: results of F1 showed that there were genetic differences between parents in the studied traits and significant and highly significant values measured to mid parents in many crosses for different traits. The hybrids: Raqa5 X DP70, CIM70 X BR115 and CIM70 X BR636 showed highly significant negative values for earliness parameters. While a highly significant positive values were found in following crosses: Deir Ezzor 22 X BR 636 for number of fruit brunches/plant, Deir Ezzor 22 X DP 41 for lint percentage, DP70 X BR 636 for boll weight average, Aleppo118 X BR 115 for fiber strength and Deir Ezzor 22 X BR 636 for fineness and elongation.
On the other side, insignificant heterosis appeared in some traits, as fiber length and plant height.
The dominance degree: the ratio of variance components of GCA to variance components of SCA was >1 for the traits: maturity date, lint percentage and technologic traits. This refers to the dominance of additive gene action.
While this ratio was <1 in the traits: flowering date, boll weight average, number of total bolls/ plant, number of remained bolls/ plant and shedding percentage characterized by dominance of the variance of SCA.
This reflects the dominance of non-additive gene effect.
-General Combining Ability (GCA): Studding of GCA showed that the parental genotype Aleppo 90 has a high GCA for earliness, Aleppo 118 for the average of b0ll weight, Raqqa 5 and CIM 70 for fiber length. DP 41, BR 115 and BR 636 for lint percentage, number of total bolls/ plant and number of remained bolls/ plant.
This refers that these parents have the largest number of additive genes which control these traits.
– Specific Combining Ability (SCA): Estimates of SCA values were significantly different, the results showed that the hybrids resulted from parents which have a positive significant GCA, had significant and highly significant effects of SCA and the type of Gene Action is (additive X additive), as the following:
– Aleppo 90 X Aleppo 118, Aleppo 90 X CIM 70 and Aleppo 118 X Raqa5 for earliness.
– Aleppo 90 X DP 41, Aleppo 118 X, Deir Ezzor 22, Raqqa 5 X Deir Ezzor 22 and Raqqa 5 X CIM 70 for the average of b0ll weight and fruit brunches number\plant.
– Deir Ezzor 22 X BR 115, Tashqend 6 X BR 636 and BR 115 X BR 636 for lint percentage.
– Aleppo 118 X CIM 70, Aleppo 118 X BR 636, CIM 70 X BR 636 and CIM 70 X DP 41for technological characters.
– Raqqa 5 X DP 41, Deir Ezzor 22 X DP 41, Deir Ezzor 22 X BR 636 and DP 41X BR 115 for number of total bolls\plant and number of remain bolls\plant.
– Heritability ratio: The estimating of the heritability ratio is an important parameter because it determines the efficiency of the selection, which decreases as this scale decreases. The heritability ratio was variable for the deferent traits, as following:
– Too high: For days to maturity (85%), lint percentage (99%), fiber length (94%), fiber fineness (96%) and shedding percentage (86%).
– High: Days to budding (69%), plant height (65%), fiber strength (77%), and number of remained bolls/ plant (70%).
– This refers that the genetic action is the most effective factor in the inheritance of these traits.
– Moderate: boll weight average (54%) and elongation (45%).
– Low: number of fruit brunches/plant (30%).
This refers that the environmental difference is the most effective factor in the inheritance of these traits.
– Shedding percentage:
-Tel-Temr\ F1: Aleppo 118 had the highest rate of shedding, and lest rate was in Tashqend 6 and BR 115. In hybrids Aleppo 118 X DP 41 had the highest shedding rate, and lest rate was in Raqqa 5 X Deir Ezzor 22 and – Tashqend 6 X CIM 70.
-Tel-Temr\ F2: Aleppo 118 had the highest rate of shedding, and lest rate was in Tashqend 6 and Raqqa 5. In hybrids Aleppo 90 X Aleppo 118 had the highest shedding rate, and lest rate was in Raqqa 5 X Deir Ezzor 22 and Tashqend 6 X CIM 70.
– Deir Ezzor \F1, F2: Aleppo 118 had the highest rate of shedding, and lest rate was in Tashqend 6 and Deir Ezzor 22. In hybrids Raqqa 5 X DP 41 had the highest shedding rate, and lest rate was in Deir Ezzor22 X DP 70 , Tashqend 6 X BR 115 and Tashqend 6 X BR 636.
Laboratory study: The results showed that the pollen validity in parents and hybrids wasnt affected at 25-28 C, and the germination ratio obviously varied at 30-32 C in parents and hybrids. Raqqa 5 was the best and Aleppo 118 the worst. In hybrids Tashqend 6 X DP 41 was the best and Aleppo 90 X Aleppo 118 the worst. While at 35 C and more the pollen validity was negatively affected in all parents and hybrids.