Abstract: CRIS-7A as jassid resistant variety requiring one or two less insecticide applications for control. However maximum population of whitefly was observed on this variety indicating the positive correlation of hairiness and whitefly attack. CRIS-7A recorded minimum bollworm damage percent as compared to commercial checks NIAB-78 and CRIS-9. CRIS-7A also has proved as boll rot disease resistant and seedling rot disease tolerant variety when compared with other advance strains and standards. This variety has proved itself among the high yielding varieties also.
Introduction
Many cotton growers depend on chemical insecticides for controlling jassid. However, the use of pesticides has led to problems such as development of resistance and resurgence of secondary pests. Therefore there is need for exploring alternate methods to manage this pest. The cultivated cottons, G. arboreum and G. tomentosum, G. armourianum and G. raimondii are resistant to jassid (Narayanan and Singh, 1994). The hairiness in these wild species is attributed for the resistance of jassid (Santhanam, 1958). Development of varieties resistant to sucking pests especially jassid, remained the significant feature of the research conducted for cotton protection in India and Pakistan since long. Shah (1974) found M-4 slightly resistant, Qalandri (H-59-1) and S-61-30/8 resistant and M-100, Sarmast (S-59-1) and S-64-15 as the most susceptible to jassid. He also expressed that resistant varieties are more hairy than susceptible ones. Javed (1994) studied the resistance of upland cotton to jassid in selection to hairiness on cotton varieties of Sindh and concluded that all the varieties showing resistance were hairy. Hussain (1984) indicated that hair density and length of hair on abaxial surface of the leaf are the major factors, which contribute to jassid resistance. Agarwal at al. (1978) reported that leaf hairiness is the only recognizable morphological attribute, which is closely linked with resistance of jassid. They also explained various mechanisms of resistance to jassid in cotton by reviewing different morphological, anatomical and biochemical basis of resistance. Ahmed (1980) opined that hair density of mid rib, leaf lamina and length of hair on mid rib and lamina contribute towards resistance to jassid and susceptibility to whitefly. Referring the previous studies on jassid resistance, Central Cotton Research Institute, Sakrand exploited hairiness character extensively and developed a new densely hairy variety CRIS-7A through conventional breeding by crossing densely hairy variety Rajhans from India and local variety NIAB-78. These studies were under taken to assess CRIS-7A against insect pest resistance, yield and fiber quality characters.
Materials and Methods
CRIS-7A (densely hairy variety) which is cross between an exotic hairy variety Rajhans from India and NIAB-78 a local commercial variety. To confirm its resistance against sucking insects and bollworms, the host plant and disease resistance trials were conducted (without any pesticide application) at CCRI, Sakrand during 1997 and 1998 crop seasons. The seedcotton yield comparison trials like zonal varietal and demonstration trials were also conducted to assess the yield potential of CRIS-7A against other candidate strains and commercial varieties during 1997 and 1998 seasons. All the trials had randomized complete block design with four replications. Recommended agronomic practices (hoeing, weeding, interculturing, plant to plant and row to row spacing) including fertilizer application were carried out during the experimentation period.
Results and discussion
Host plant resistance trial: Minimum population of trips and jassid was recorded from CRIS-7A (Table 1) that hairiness provides resistance against jassid.
The maximum population of these pests (trips and jassid) recorded was 4.52 and 2.0 from CRIS-105 and CRIS-5A respectively. The population of trips and jassid recorded from commercial varieties CRIS-9 and NIAB-78 was significantly higher than CRIS-7A. As regards whitefly, the hairy variety CRIS-7A recorded maximum population proving positive correlation of hairiness and whitefly attack. Non-significant results were observed when bollworm damage percent was recorded. This hairy variety CRIS-7A recorded minimum bollworm damage percent as compared to commercial varieties CRIS-9 and NIAB-78.
As regards seedcotton yield, non-significant differences were observed between the varieties. None of the compared varieties/strains surpassed commercial variety CRIS-9. However, CRIS-7A with 2196 kg ha–1 surpassed other commercial variety NIAB-78 that produced 1435 kg ha–1 seedcotton yield. It can safely be concluded from the data of Table 1 that CRIS-7A is complete jassid resistant strain and also tolerate trips and bollworm attack. Being densely hairy variety CRIS-7A is susceptible to whitefly but can be listed among the high yielding varieties because it has surpassed NIAB-78 the widely grown variety in Sindh.
Disease resistance trial: CRIS-7A was found tolerant variety against seedling rot disease after CRIS-19 and CRIS-121 during 1997 and after CRIS-121 during 1998. As regards boll rot disease, CRIS-7A recorded minimum percent of the disease during both the years. When number of bolls/plant was observed, CRIS-7A produced highest bolls/plant during 1997. In the year 1998 this variety was among the second best varieties and produced 23 bolls/plant, however CRIS-121 recorded 27 bolls and ranked first during 1998. As regards seedcotton yield, on an average of two years, CRIS-7A ranked third by producing 2605 kg ha–1. The highest seedcotton yield was produced by CRIS-121 followed by CRIS-9 the standard. The second standard variety Tamcot gave 2246 kg ha–1 seedcotton yield (Table 2).
Yield Trials
Zonal Varietal Trial: The average seed cotton yield data are presented in Table 3. During 1994 CRIS-7A yielded minimum but statistically the results were non-significant. CRIS-7A ranked second in the year 1995 and was statistically at par with CRIS-9 (check) and CRIS-107. The second check variety NIAB-78 yielded lowest.
| Table 1: | Natural resistance of CRIS-7A and other newly developed strains against insect pest complex during 1997-98 cotton season at CCRI, Sakrand |
| Means followed by similar letters are not significantly different from each other according to DMR test | |
| Table 2: | Natural resistance of CRIS-7A and other newly developed strains against seedling rot and boll rot diseases during 1997 and 1998 cotton seasons at CCRI, Sakrand |
| Table 3: | Performance of CRIS-7A and other advance strains in zonal varietal trials conducted during 1994 through 1996 |
| Means followed by similar letters are not significantly different from each other according to DMR test | |
| Table 4: | Performance of CRIS-7A and other advance strains in demonstration trials during 1997 and 1998 cotton season at CCRI, Sakrand |
During 1996, CRIS-7A out yielded both commercial varieties but statistically was of the same order. On an average of three years CRIS-7A defeated NIAB-78 (check) but was slightly behind the second check variety CRIS-9. Thus keeping in view the average performance of CRIS-7A in yield comparison tile's, this hairy variety can be listed among high yielding varieties with the extra benefit of one or two reduced sprays against jassid.
Demonstration Trials: Table 4 revealed that CRIS-7A during 1997 season out yielded six varieties including two standards CRIS-9 and NIAB-78. But in the year 1998 due to very poor plant population of CRIS-7A and CRIS-79 these varieties remained far behind other varieties and two commercial checks. However CRIS-7A has proved as jassid resistant variety and requires one or two less insecticide applications against this pest.