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a Central Cotton Research Institute (CCRI), Old Shujabad Rd., Multan, Pakistan
b National Institute for Biotechnology and Genetic Engineering (NIBGE), P.O. Box 577, Jhang Rd., Faisalabad, Pakistan
* Corresponding authors (mnaveedarshad{at}yahoo.com, mehboob_pbd{at}yahoo.com).
ABSTRACT
‘CIM-496’ cotton (Gossypium hirsutum L.) (Reg. No. CV-125, PI 657627, Pak 024263) was developed by the Central Cotton Research Institute (CCRI), Multan, Pakistan, and released in 2005 for general cultivation as a part of investigations oriented toward evolving high-yielding cotton cultivars that are resistant to the cotton leaf curl virus disease (CLCuD). The cultivar was developed through crossing CIM-425 with 755-6/93. CIM-496 was tested in multiple trials conducted by various public agencies, as well as by CCRI Multan. In varietal trials conducted for three successive normal cotton-growing seasons (2000–2002) at three different sites, CIM-496 outyielded significantly all the standard varieties included in the present study. In zonal trials arranged at 26 different sites, the seed cotton yield (SCY) of CIM-496 was 11.1% and 9.8% more than checks ‘CIM-473’ and ‘CIM-499’, respectively. In the National Coordinated Varietal Trial (NCVT), CIM-496 produced more SCY than the standards for two consecutive years (2003 and 2004). CIM-496 is resistant to the Multan strain of CLCuD and also possesses a higher lint percentage compared with the existing commercial varieties. The commercial cultivation of this cultivar has substantially contributed in sustaining cotton production in Pakistan and can also be used as valuable genetic resource in future cotton breeding programs.
Abbreviations: CCRI, Central Cotton Research Institute • CLCuD, cotton leaf curl virus disease • HVI, high volume instrument • RCBD, randomized complete block design • SCY, seed cotton yield
Cotton (Gossypium spp.) is the leading natural fiber crop worldwide. In Pakistan, a cultivated cotton species G. hirsutum L. covers 
98% of the total cultivated area and contributes more than 60% of the foreign exchange (Rahman et al. 2002). Breeding efforts for improving G. hirsutum L. were initiated since its introduction in this region. In the early 1980s, new cotton varieties such as ‘Deltapine 16’ (DPL-16) were introduced in Pakistan and have been widely used to develop new high-yielding and early-maturing varieties, especially ‘S-12’. This cultivar was later banned by the Government of Pakistan because of its high susceptibility to cotton leaf curl virus disease (CLCuD). Typical symptoms of the disease are upward or downward curling of leaves and small and large thickening of the veins, which lead to the development of leaf enation, an outgrowth on the lower side of the leaves. The disease substantially depressed cotton production in Pakistan (Rahman et al. 2005). In the early 1990s, cotton germplasm was screened in hot-spot regions of Pakistan, and three cotton genotypes (CP-15/2, LRA-5166, and Cedix) conferring resistance to the disease were identified. These were extensively used to breed for disease-resistant cotton cultivars possessing high yield potential. ‘CIM-1100’ was the first disease-resistant variety, developed by the Central Cotton Research Institute (CCRI), Multan, Pakistan, and was released for general cultivation in 1996 by the Punjab Seed Council. Later, a series of virus-resistant cultivars were released, including CIM-1100, ‘CIM-448’, ‘CIM-473’, ‘CIM-499’, ‘FH-901’, ‘FH-900’, and ‘FH-1000’, which were of marginal yield potential.
In Pakistan, there is a focus on improving cotton germplasm and cultivars that can combat drought stress (Rahman et al. 2008; Ullah et al. 2008), exhibit resistance to the CLCuD (Rahman et al. 2002; 2005), and possess higher yield potential with improved fiber traits (Soomro et al. 1986; Khan et al. 1989; Afzal et al. 2001; Hanif et al. 2001; Arshad et al. 2003). Hence, most research efforts were diverted to evolve cultivars that were not only showing high yield potential in different agroclimatic zones with acceptable fiber characteristics but also resistant to the disease as a step toward sustaining cotton production in Pakistan. Thus, cotton cultivar CIM-496 (Reg. No. CV-125, PI 657627, Pak 024263) was developed, exhibiting desirable features coupled with high lint production. It was cultivated on more than 42.90% of the total cotton growing area of Pakistan in 2006 (Table 1 ). The commercial release of this cultivar has significantly contributed to overall cotton production in the country. In the present study, its unique features are discussed.
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The new cotton cultivar CIM-496 was developed through making the cross CIM-425/x/755-6/93 in 1993 at CCRI Multan. The genotype CIM-425, developed at CCRI, has a high yield potential, semideterminant growth habit, and desirable fiber characteristics; however it is susceptible to the virus disease. It was developed from a cross between CIM-70/CIM-158. The male parent 755-6/93 (W-1104/S-12//CP-15/2) is extremely resistant to the Multan strain of the virus, has exhibited high heat tolerance, and is also early maturing. Around 50 F1 plants were grown in the disease sick block of the cotton field of CCRI Multan and were self-pollinated to harvest F2 seed from each plant. The F2 plants along with spreader rows of variety S-12 (every third row) were raised in the mid of June at the cotton field of CCRI Multan for ensuring maximum infection of the disease (Rahman and Zafar, 2007). Moreover, chemicals were not sprayed to control the vector population (whitefly [Bemisia tabaci]) up to 90 d. The F2 plants and the succeeding generations were also petiole grafted with infected buds by the T-shape grafting method to provide maximum inoculum of the virus (Rahman et al., 2005). The grafted buds were wrapped with a polyethylene strip to minimize the chances of evaporation. The process was preferably done in the evening hours. The plants were observed daily, and the plants resistant to CLCuD were selected to advance the generation (Rahman et al., 2002).
The field-grown F3 plant progenies of the virus-free F2 plants were exposed to the disease inoculum by ensuring maximum whitefly population and also through the grafting of infected buds. The F3 progenies that were nonsegregating for disease resistance and also exhibited acceptable yield potential and fiber traits were advanced to the F4 generation. The procedure was repeated until F5. In 1999 to 2000, one of the F5:6 progenies that was resistant to the disease and showed acceptable yield potential was selected and designated as CIM-496.
In the following seasons (2000 through 2002), yield potential and other morphological traits of CIM-496 were compared with commercial varieties (CIM-499, FH-900, CIM-473, and CIM-446) at three sites (CCRI Multan, Punjab Seed Corporation, Khanewal and Kot Addu, Pakistan). At each site, we followed the randomized complete block design (RCBD) with four replications (size of the each plot was 56 m2). Standard agronomic practices were applied from sowing to harvesting. At maturity, seed cotton was hand-picked from the plants of two central rows for determining the seed cotton yield (SCY) potential of each genotype. Similarly, zonal trials at 26 diverse locations including farms of progressive growers of the Punjab province were sown in 2003. All the trials were arranged in an RCBD with four replications, with cultivars CIM-499 and CIM-473 included as checks. Standard agronomic practices were followed from sowing to harvesting at all locations.
Data of various morphological traits such as number of monopodial and sympodial branches per plant, plant height (cm), boll weight (g), and boll number were recorded at maturity. Average number of monopodial and sympodial branches per plant was calculated by counting them from 20 consecutive plants from each plot. Similarly, plant height was recorded in centimeters from the first cotyledonary node to the apical bud. Seed cotton from five consecutive plants was picked and total number of bolls was counted. The average boll weight was determined by dividing the total seed cotton weight by the total number of bolls picked from these plants. The number of bolls per plant was calculated by counting the number of bolls on each plant from the five consecutive plants from each plot. Seed cotton yield was recorded from the two central rows. Seed cotton was hand-picked 180 d after sowing and was sun-dried after removing the trash before weighing. The seed cotton was ginned out with a small laboratory-scale saw gin for determining the lint percentage and fiber quality traits. Lint percentage was calculated by dividing the weight of the lint sample after ginning by the weight of the total seed cotton and multiplying by 100. A lint sample size of 50 g was taken to measure the fiber length, fiber strength, uniformity index, and micronaire value using a high volume instrument (HVI).
CIM-496 was also tested at 11 and 15 diverse locations of Pakistan in the National Coordinated Varietal Trial (NCVT) in 2003 and 2004, respectively, conducted by the Pakistan Central Cotton Committee, Karachi, Pakistan (a semiautonomous organization). Each of the field trials was arranged in an RCBD with four replications. The size of the plot in each replication was 56 m2 (12.2 by 4.6 m). Standard agronomic practices were followed.
For determining the response of CIM-496 to the CLCuD and its comparison with the checks (CIM-473 and CIM-499), a total of 200 plants were planted in mid-June along with the spreader rows of S-12 (every third row). Disease symptoms were recorded fortnightly. These varieties were also grafted by a procedure as described in an earlier section.
Infestation level of sucking insect pests was determined through counting the number of nymphs and adults of jassid (Amrasca devastans), whitefly, and thrips separately from 10 randomly selected leaves from upper, middle, and lower position of the plants from each replicate. Number of insects per leaf was calculated by dividing the total number of individuals of each insect species by the total number of leaves examined. Similarly, infestation by bollworms (Helicoverpa zea) was determined by counting the number of fruiting bodies damaged by bollworms in a four randomly selected 132-cm lengths of row and dividing them by the total number of fruiting bodies observed.
Analysis of variance was performed on each measured trait using appropriate procedures of the MSTAT-C computer software package. Statistical significance was reported at a 5% level of probability. Differences among means were tested by the least significant difference test at the 5% probability level.
Characteristics
CIM-496 was tested in replicated varietal trials conducted at the field of CCRI Multan and two substations located in Khanewal and Kot Addu, for three consecutive years (2000, 2001, and 2002) (Table 2 ). In 2000 the mean SCY of CIM-496 was 3666 kg ha–1 compared with 3052 kg ha–1 for FH-900 and 3194 kg ha–1 for CIM-446. In 2001 the SCY of CIM-496 was 3764 kg ha–1 compared with 3572 (CIM-473), 3207 (CIM-482), 3242 (FH-900), and 3279 kg ha–1 (CIM-446). Similarly, during 2002 to 2003, CIM-496 outyielded both the checks, CIM-473 and CIM-446.
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Evaluation for Morphological and Fiber Traits
CIM-496 (119.20 cm) was taller than CIM-499 (115.60 cm) and CIM-473 (112 cm). The number of monopodial branches of CIM-496 was more than that of CIM-499 but similar to CIM-473. The number of sympodial branches per plant of CIM-496 was more than either of the checks (Table 6
). Average boll weight of CIM-496 was 3.1 g, compared with 3.2 g for CIM-499 and 3.3 g for CIM-473. The number of bolls per plant was 47.3 for CIM-496, 42.3 for CIM-499, and 38.0 for CIM-473 (Table 6).
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2 to 3% lower than the standards. The uniformity index of CIM-496 was 84.5% compared with 84.3% for CIM-499 and 84.1% for CIM-473 (Table 6). CIM-496 is of the spreading type with medium to light green foliage. The leaves are of normal shape and are nectaried. CIM-496 is glanded and has a pubescent stem and leaves. The pollen color is creamy, and the boll shape is round pointed. CIM-496 is well adapted to many types of environments, and its outstanding yield in farmer's fields in the Punjab Province is the reasons for its high acceptability among the farming community (Table 1). This cultivar would be an excellent candidate for doing value addition work through nonconventional means. This cultivar is suited for introducing Cry1 Ac and other genes conferring resistance to chewing insect pests, which will set a stage for sustaining cotton production in the future.
Availability
Limited quantities of CIM-496 seed for research purposes can be obtained from the corresponding authors. Appropriate recognition of the source should be given when it contributes to the development of new cultivars, breeding lines, or hybrids.
Acknowledgments
The funds for the development of CIM-496 were provided by the Ministry of Food, Agriculture and Livestock (MinFAL), Islamabad. We are thankful to Dr Ibad Badar Siddiqui, former Vice President (VP), Pakistan Central Cotton Committee (PCCC), Karachi, for providing logistic support in the development of this cultivar. We are extremely grateful to the Section Heads of CCRI (Plant Pathology, Entomology, Agronomy, Physiology, Statistics, and Fiber Technology) for generating useful data. The cooperation extended by Mr. Muhammad Umar, Director of Punjab Seed Corporation, Khanewal, during testing and seed multiplication is also highly acknowledged. Special thanks to Dr. Zahoor Ahmad Baluch, Vice President (former Director of Research), PCCC, Karachi, for testing this variety in NCVT. Finally, we appreciate the role of Punjab Agricultural Research Board (PARB), Lahore, for providing us funds to publish this manuscript.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication April 6, 2009.
References
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