ABSTRACT No information regarding pathogenic variability among different isolates of Ralstonia solanacearum infecting chili from different agro-ecological zones of Pakistan with varying climatic and edaphic factors is available. Therefore, in the present study, variations were observed in biovar distribution, hypersensitive response, growth and virulence among 114 isolates of R. solanacearum collected from eight agro-ecological zones of Pakistan. Out of 114 R. solanacearum isolates, 81% were identified as Biovar III, while the remaining 19% were recognized as Biovar IV. Of all the 114 isolates of R. solanacearum, 77% showed positive hypersensitive response and mucoid growth, while 23% isolates gave negative hypersensitive response with non-mucoid growth. Out of 114 isolates of R. solanacearum consisting of Biovar III and IV, 22.8% were found avirulent, 25.4% weakly virulent, 29.8% virulent, and the remaining 21.9% were highly virulent. Variations among 114 R. solanacearum isolates were also observed in four provinces of the country. Among 92 R. solanacearum Biovar III isolates, 21.7% were identified as avirulent, 25% weakly virulent, 34.4% virulent, and 22.8% were highly virulent in the eight agro-ecological zones of the country. Similarly, out of 22 R. solanacearum Biovar IV isolates, 27.3% were detected as avirulent, weakly virulent and virulent, while 18.2% isolates were found highly virulent. The isolates having non-mucoid growth and negative hypersensitive response were found avriulent, while those with mucoid growth and positive hypersensitive response were weakly virulent to highly virulent. The information will help design control strategies accordingly and develop resistant cultivars against the bacterium.

ABSTRACT The production of chili is seriously threatened by bacterial wilt incited by Ralstonia solanacearum in Pakistan. As the information about the distribution and prevalence of the disease and the pathogen is scarce, the present study was performed to ascertain the prevalence, occurrence and distribution of R. solanacearum in different regions of chili cultivation. The results showed differences in the incidence and prevalence of bacterial wilt all over the country. Overall, an incidence of 10% and prevalence of 76% of the disease was observed in the country. The highest incidence of bacterial wilt was observed in the province of Sindh whereas it was the lowest in Baluchistan. The prevalence of the disease followed the similar trend in the provinces. As regards agroecological zones, the highest incidence was recorded in Indus delta followed by sandy deserts whereas it was the lowest in western dry mountains. Almost the same tendency was observed regarding prevalence in the eight agroecological zones. In case of districts, the disease incidence was the maximum in Badin while it was the minimum in the district of Loralai. On the other hand, the disease prevalence was the maximum (100%) in the districts of Badin, Mirpurkhas, and Thatta and the minimum (60%) in the districts of Barkhan, Karak, and Loralai. Of the total 114 isolates of R. solanacearum, 81% were confirmed as Biovar 3 whereas the rest 19% isolates were identified as Biovar 4. The findings will help the farmers to design disease management programs accordingly to avert yield losses.

ABSTRACT For proper disease management, accurate diagnosis of the pathogen is essential. Therefore, in the present study Ralstonia solanacearum causing bacterial wilt of chili was characterized to determine the distribution of biovars of the bacterium in the eight agroecological zones with varying climatic conditions and edaphic factors. Among all the 114 isolates of R. solanacearum, 77% showed mucoid growth while 23% isolates gave non-mucoid growth. Similarly, the isolates with mucoid growth were found positive for hypersensitivity response (HR), while those with non-mucoid growth showed negative HR. All the isolates grew well at 37 °C, while none of the isolates produced its colony at 41 °C. All the 114 isolates of R. solanacearum showed positive responses for all the biochemical tests used for confirmation of the bacterium. Out of 114 R. solanacearum isolates, 81% were identified as Biovar III while the remaining 19% were recognized as Biovar IV. Biovar III constituted 37 and 70% in the provinces of Punjab and Sindh, respectively, while Biovar IV formed 19 and 30%. On the other hand, in Khyber Pakhtunkhwa and Balochistan, only Biovar III was recorded. Similarly, Biovar III was observed from all the eight agroecological zones of the four provinces of the country and found to be predominant. On the other hand, Biovar IV was recorded from four agroecological zones located in the provinces of Punjab and Sindh. All the isolates yielded a 750-bp band that corresponded to R. solanacearum. It is concluded that Biovar III is widely prevalent in the country warranting stringent control measures.

ABSTRACT One of the most effective and cost-efficient methods to manage plant parasitic nematodes is to use resistant cultivars. However, little information on the resistance of commercial okra cultivars grown in the country was available. Therefore, nine okra cultivars were evaluated for their comparative resistance against Meloidogyne incognita, the most damaging root-knot nematode. None of the tested okra cultivars showed high level of resistance. However, three cultivars viz. Pusa Swami, PB Selection and Green Star appeared as moderately resistant. Sabz Pari, Neelum and Tulsi were found moderately susceptible to the nematode. Two cultivars i.e. Ikra-1 and Ikra-2 were susceptible and Arka Anamika was highly susceptible. The okra cultivars differed significantly in their growth parameters depending on their response to M. incognita. Moderately resistant cultivars sustained little damage as compared to moderately susceptible or susceptible cultivars while the highly susceptible cultivar suffered the maximum damage by the nematode. Significant differences in the numbers of galls, eggmasses and reproductive factors of M. incognita on the nine okra cultivars were also observed. The highest numbers were found on Arka Anamika, followed by Ikra-1 and Ikra-2. The lowest numbers were found on the moderately resistant cultivars, followed by the moderately susceptible ones. High and positive correlations between the number of galls and eggmasses and the decreases in growth metrics were found using linear and non-linear regression analysis.

ABSTRACT The widespread use of transgenic plants imposes selection pressure on insect pest populations to develop insecticide resistance. Evaluation of effectiveness of resistance management strategies is very important in resistance management programs. Resistance management to insecticides is widely believed to depend in part on associated fitness costs. Fitness costs can delay the development of resistance. In the present study, the effects of two entomopathogenic nematode species, Steinernema carpocapsae and Heterorhabditis bacteriophora were studied on the fitness of first insect population of Heliothis virescens selected with Vip3A in the laboratory. It was found that both nematodes species increased the fitness cost of Vip3A selected insects. The mortality of the Unsel subpopulation after exposure to either nematode species was significantly lower than that of the Vip3A-Sel subpopulation. Likewise, the reproduction of both nematode species was significantly greater in cadavers of the Unsel compared with the Vip3A-Sel subpopulation of H. virescens. There was positive correlation between nematode reproduction and the larval instar infected with nematodes. The penetration of infective nematode juveniles (IJ) was greater in the Vip3A-Sel subpopulation than in the Unsel subpopulation of H. virescens. It is concluded that entomopathogenic nematodes could increase the fitness costs and subsequently delay the resistance.

ABSTRACT In the present study, the damaging effects of six inoculum densities of Meloidogyne incognita were compared on a resistant (Long Green) and a highly susceptible (Mirage) cultivar of cucumber. All the inoculum densities of M. incognita resulted in significant reductions in growth and yield variables of both the cultivars over their controls. The reductions in resistant cultivar were significantly lower as compared to the highly susceptible cultivar at all inoculum levels. The highest inoculum level caused the maximum reductions in growth and yield variables while the lowest inoculum level resulted in the minimum reductions. The reductions in growth and yield variables increased with an increase in the inoculum density showing a positive relationship. On the other hand, the inoculum levels caused an increase in root weight. The higher inoculum levels caused higher increases while at lower inoculum levels, the increases were lower. The increases in root weights were significantly lower in the resistant cultivar when compared to the highly susceptible one showing a direct relationship between the increase in root weight and inoculum levels. Similarly, significant differences in number of galls and egg masses were noticed between the resistant and highly susceptible cultivar at all inoculum levels. The galls produced on highly susceptible cultivar were significantly higher as compared to the resistant one. A direct relationship was observed between inoculum levels and number of galls and egg masses. On the other hand, all the inoculum levels varied significantly regarding reproductive factor on the resistant and highly susceptible cultivars.

ABSTRACT Meloidogyne incognita is one of the most widespread and damaging plant-parasitic nematodes throughout the world and substantially affects growth and yield of okra (Abelmoschus esculentus L). In the present study, effects of M. incognita on yield parameters of 12 okra cultivars with varying levels of resistance or susceptibility were assessed. M. incognita caused significant reductions in yield parameters of okra plants of all the cultivars. Maximum reduction of 34.1% in yield was observed in highly susceptible (HS) cultivar Sharmeeli. The nematode caused 20 and 17.6% reductions in yields in susceptible (S) cultivars Okra Sindha and Anmol, respectively. Moderately susceptible (MS) cultivars suffered 5.9 to 12.9% reductions in yields. In case of moderately resistant (MR) cultivars (Sanam, Dikshah, Arka Anamika, Ikra-1 and Ikra-2), the reductions in yields were the minimum and ranged from 2.9 to 6.5%. The reductions in other yield parameters of okra cultivars were observed in the order HS > S > MS > MR. As the MR cultivars suffered less damage by the nematode, they are recommended for cultivation in fields heavily infested with M. incognita.

ABSTRACT Loquat is attacked by many phytopathogenic fungi. Among these Spilocaea pyracanthae is of economic importance. The fungus received no attention in Pakistan and some other parts of the world. The current study is focused on the symptomatology of this disease and the etiology of the fungus. During extensive surveys of loquat orchards in 2013 heavy infestations of this disease were observed. The leaf symptoms were observed as olive brown, opaque necrotic sub-circular spots, with light brown coloration in the center. Two or more spots coalesced in severe infections covering large leaf areas. The fungus was identified as Spilocaea pyracanthae on the basis of conidia and morphological characters. The pathogenicity of the fungus was confirmed on healthy plants under greenhouse conditions by following Koch's postulates. The fungus produced characteristic leaf scab symptoms on young leaves. This is the first report of Spilocaea pyracanthae causing leafscab of loquat in Pakistan.