Syed Jawad Ahmad Shah

Characterization of Slow Rusting Resistance against Puccinia striiformis f. sp. tritici in Candidate and Released Bread Wheat Cultivars of Pakistan

A set of 50 candidate and released bread wheat cultivars of Pakistan were studied to identify slow rusting resistance against yellow rust caused by Puccinia striiformis f. sp. tritici (PST). Seedling tests were done under glasshouse conditions at Thiverval-Grignon, INRA, France while slow rusting resistance was evaluated during 2005-07 in field plots using epidemiological variables at Peshawar, Pakistan. Twenty nine cultivars (58%) displayed susceptibility against the two PST races used in the seedling tests. Epidemiological parameters of resistance at the adult-plant stage were significantly (P<0.01) different for years, cultivars and cultivar x year interactions over three years. Analyses were done for sequence tagged site (STS) marker, csLV34 at INRA and revealed that 40% of the tested cultivars possessed adult plant resistance gene Yr18 linked allele of 150 bp. Of the 50 cultivars evaluated under field trials, 11 were highly resistant to both PST races as in the seedling tests and 39 showed different levels of slow rusting. Cultivars Bakhtawar-93, Punjab-96, Bahawalpur-95, V-00183 and V-00125 were relatively more stable over 3-years as Final Rust Severity (FRS), Area Under Disease Progress Curve (AUDPC) and Infection Rate (r) values were 74, 81, and 63% less of the susceptible control, Morocco, respectively. These cultivars also possessed the marker linked to Yr18 and could be exploited for the deployment of Yr18 in breeding for slow rusting in wheat. Both FRS and ACI are suitable parameters and can be used for phenotypic selection in a wheat breeding program for slow rusting resistance.

A Review on Barley Yellow Dwarf Virus

Barley yellow dwarf (BYD) is an economically important, most widely distributed, and destructive viral disease of cereals. The disease is caused by barley yellow dwarf virus (BYDV). The virus is phloem-limited pathogen and causes variable symptoms depending upon the virus isolate, crop species, time of infection and environmental conditions. In general, yellowing and reddening of leaves starting from upper tips to downward, dwarfing and reduction in size and number of ears and grains are observed in infected plants. BYDV is an isometric Luteovirus containing ssRNA genome and is transmitted in a persistent manner by more than 20 species of aphids. The disease has a serious economic impact and yield losses are variable and may range from 5% to 50%. Presently, five isolates of the virus such as PAV, MAV, RMV, RPV and SGV have been identified based on epitope profile and aphid vector specificity. The five biologically well defined isolates are sub-divided in two sub-groups; subgroup 1 including PAV, MAV and SGV and subgroup 11 including RMV and RPV. Although the disease can be managed by integrated approaches such as cultural practices, use of pesticides and host plant resistance, but planting of crop varieties with tolerance or resistant is the most economical and practical approach. Development of host plant resistance through genetic engineering is another possible option to combat the problem. Recombinant DNA technology has opened up the prospect of increasing genetic diversity in crop plants by their transformation. This will further help to increase the genetic resistance of bread wheats while using BYDV-resistant genes already identified in wild relatives of wheat and other species. Given the economic significance of the disease and its world wide occurrence, this review has been presented to update the knowledge of various aspects of BYDVs.