Publications

4366

Malakand Division in northwest Pakistan is known for delicious sweet orange, locally called Malta (Citrus sinensis). However, both quality and quantity of the citrus produce has seen a decline over the past few decades. Among production constraints, Huanglongbing (HLB) caused by phloem-limited alpha proteobacterium Candidatus Liberibacter asiaticus (CLas) -an endosymbiont of Asian Citrus Psyllid (Diaphorina citri), is of great economic significance. Therefore, we assessed HLB incidence through symptom-based surveys in major citrus growing areas of Khyber Pakhtunkhwa (KP), Northwest Pakistan. The presence or absence of CLas in the collected citrus samples was confirmed by PCR (Polymerase Chain Reaction) using three set of primers (LSS/LAS606, OI1/OI2C “16S rDNA” and MH353/MH354 “operon “nusG-rplK”). An average disease incidence of 92% and severity of 34% were recorded from main production zones in district Swat, KP. Likewise, in district Lower Dir, HLB had disease incidence and severity of 64% and 24%, respectively. Molecular diagnostics using 16S rDNA-specific primer LSS/LAS606 and OI1/OI2C, yielded characteristic bands of 500 bp and 1160 bp, from all five pooled samples from Swat district, while only two samples of Dir tested positive for both primers. Using an alternative primer MH353/MH354 (nusG-rplK) showed positive amplification for four samples from Swat and two samples of Dir with an amplicon of 631 bp. To assess the molecular diversity of the CLas, Sanger sequencing was carried out based on16S rDNA gene. Sequence analysis of 16S rDNA gene from all samples revealed maximum similarity with C. Liberibacter asiaticus. Among studied isolates, SwKjuPk-5 (MH374503) and SwMtaPk-2 (MH374500) isolates appeared to be more divergent and grouped in separate clad as compared to remaining isolates of Swat and Dir. 

AbstractBois noir, a disease of the grapevine yellows complex, is associated with ‘CandidatusPhytoplasma solani’ and transmitted to grapevines in open fields by the cixiidsHyalesthes obsoletusandReptalus panzeri. In vine-growing areas where the population density of these vectors is low within the vineyard, the occurrence of bois noir implies the existence of alternative vectors. The aim of this study was to identify alternative vectors through screening of the Auchenorrhyncha community, phytoplasma typing bystampgene sequence analyses, and transmission trials. During field activities, conducted in Northern Italy in a vineyard where the bois noir incidence was extremely high, nine potential alternative insect vectors were identified according to high abundance in the vineyard agro-ecosystem, high infection rate, and harbouring phytoplasma strains characterized bystampgene sequence variants found also in symptomatic grapevines. Transmission trials coupled with molecular analyses showed that at least eight species (Aphrodes makarovi,Dicranotropis hamata,Dictyophara europaea,Euscelis incisus,Euscelidius variegatus,Laodelphax striatella,Philaenus spumarius, andPsammotettix alienus/confinis) are alternative vectors of ‘CandidatusPhytoplasma solani’ to grapevines. These novel findings highlight that bois noir epidemiology in vineyard agro-ecosystems is more complex than previously known, opening up new perspectives in the disease management.

Potato psyllid (Bactericera cockerelli) is one of the most important pests in potatoes (Solanum tuberosum L.) due to its feeding behavior and the transmission of a bacterium (Candidatus Liberibacter solanacearum) that causes zebra chip disease, altering the quality of the potato tuber and the fried potato chip or french fry. This pest is thus a threat to the chip potato industry and often requires preventive measures including the use of costly insecticides. The objectives of this research were to monitor the variation in B. cockerelli adult abundance and to evaluate the risk of zebra chip disease in northwestern New Mexico, USA. Yellow sticky traps were used to collect the pest at the Agricultural Experiment Station at Farmington, NM and in nearby commercial fields at the Navajo Agricultural Products Industry (NAPI) and Navajo Mesa Farms during the 2017–2019 period. The collected adult pests were analyzed at Texas A & M University for the presence of Candidatus L. solanacearum (Lso). The results showed field infestation by B. cockerelli in early June and that the population peaked during the second half of July and decreased as the potato growing season progressed. However, a second less important peak of the pest was revealed around mid- to late-August, depending on the growing season and field. While the B. cockerelli population increased linearly with average air temperature, it showed strong third order polynomial relationships with the accumulated thermal units and the Julian days. The test of B. cockerelli for the Lso infection revealed a low incidence of the pathogen varying from 0.22% to 6.25% and the infected adult B. cockerelli were collected during the population peak period. The results of this study may be helpful to potato growers in pest management decision-making and control. However, more study is needed to evaluate zebra chip disease in terms of its prevention and economic impact, and to develop economic thresholds and pest management programs for northwestern New Mexico and neighboring regions.