Battling Bacterial Blight: How Rice Varieties and Wild Species Fight Back | InformativeBD

Abdul Waheed,  Habib Ahmad,  Fida. M. Abbasi,  Azhar H. Shah,  Hamid Ali,  F. S. Hamid, and Saqib Mumtaz,  from the different institute of  Pakistan. wrote a Research Article about, Battling Bacterial Blight: How Rice Varieties and Wild Species Fight Back. Entitled, Resistance Characterization of Cultivated Varieties and Rice Wild Species in Response to Bacterial Blight. This research paper published by the Journal of Biodiversity and Environmental Sciences | JBES. open access scholarly research journal on Biodiversity. under the affiliation of the International Network For Natural Sciences| INNSpub. an open access multidisciplinary research journal publisher.

Abstract

Bacterial leaf blight (BB) of rice caused by (Xanthomonas oryzae pv oryzae) is converting into a critical threat almost in all rice growing countries of the world. In order to catagorize resistant sources to virulent isolates of BB, an experiment comprising 02 species of wild rice (Oryza sp.) and four most common cultivated varieties i.e., Bas-385 , Swat-1 , JP-5 and Fakhar Malakand of rice in Pakistan was conducted in the green house of Genetic Department Garden campus ,Hazara University in the rice growing season during 2012. Bacterial suspension of concentration 108 CFU/ml was prepared from mixture of (Xanthomonas oryzae pv oryzae) prevailing in Khyber Puktunkhawa,Pakistan i.e., X00-1, X00-2 and X00-3. Clip method of artifical inoculation was used. Both tested wild relatives of rice O. longistaminata and O. rufipogon showed highly resistance to all the isolate. F3 genotypes Bas-385 x O. rufipogon was found highly susceptible to most of the isolates among all others genotypes. The use of resistant wild species O. rufipogon is therefore recommended in rice breeding program for transfer of bacterial blight resistant genes to cultivated varieties to enhance the relative characters.

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Introduction

Rice (Oryza sativa L.) is known as a staple food for more than half of the world’s population (Chakravarthi & Naravaneni, 2006). Pakistan is an important rice growing and exporting country. Pakistani Basmati rice is famous for long grain aromatic character all over the world. International Rice Research Institute reported that, export share of Pakistani rice was 10 % of the total world rice trade (IRRI, 1993).

Many diseases of rice crop significantly reduce the yield and quality all over the world, among them the bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Akhtar, 2005) is the most destructive and critical disease of rice throughout the world (Mew, 1987). This disease was first observed by farmers in Japan during 1884-85 and its occurrence has been reported in Australia, Bangladesh, India, Mainland China, Malaysia, SriLanka, Thailand, Philippines, USA, West Africa and Vietnam (Ezuka & Kaku, 2000). Mew & Majid, 1977) reported its incidence in Pakistan and it was confirmed from all the provinces in a later study (Akhtar & Akram, 1987). Recently an alarming increase in BB incidence is observed in Pakistan especially in Punjab which is largest growing province of Pakistan and famous for rice cultivation (Khan et al., 2000 & Akhtar et al., 2003). Bacterial blight appears at all growth stages of rice and is manifested by either leaf blight or “Kresek” symptoms. The causal organism invades plants through water pores and wounds (Tabei & Mukoo, 1960). Since the water pores are located at the margins of upper parts of the leaf, the lesion starts from the leaf margins near its tip. As the disease progresses, the tiny water soaked lesions turns yellow, enlarges in size progressively and develop into an elongated irregular lesion with wavy margins. Bacterial ooze, which consists of small, yellowish, spherical masses, may sometimes be seen on the margins or veins of the freshly infected leaf under moist conditions. with the passage of time, the lesion may cover the entire blade, which turns white and later greyish owing saprophytic growth (Ou, 1985).

If plant ever produces panicles, it results in sterile immature grains, which are easily broken during milling. The reduction in yield in case of severe infection could be as high as 50% (Mew et al., 1993) whereas 10-12% yield reduction has been recorded in case of mild infection (Ou, 1985). The disease is also characterized by a systemic infection phase, which is manifested by acute wilting of young plants. This is commonly referred to as “Kresek” phase. The causal organism consists of straight rods, with a single polar flagellum, occurring singularly, in pairs and sometimes in chains as well and is also Gramnegative (Swings et al., 1990). The bacterium over winters either in weeds or in soil. Grains, straw and rice stubble are other possible sites of over wintering of the pathogen. During growing season, it enters the plants via natural opening or wounds where it survives and multiplies in plant’s vascular system, producing typical leaf blight symptoms.

Bacterial bight has the potential to become a destructive disease of rice in Pakistan. Generally, the use of resistant cultivars is the most effective method for controlling plant diseases. However, the available rice germplasm in the country is susceptible to virulent isolates of bacterial blight (Akhtar, 2005). Rice productivity is limited by several biotic and abiotic stresses. Thus, there is an urgent need to wide extent the gene pool of cultivated rice. Rice wild species are an important source of variability for resistance to all major diseases, insects and pests, offered an important source of innovative resistance genes for rice crop improvement (Eizenga et al., 2009). Wide hybridization between Oryza sativa (AA genome) and wild species of rice is one of the important way to transfer genes to cultivated rice. Apart from other research innovation some useful important genes have successfully been transferred from wild species of rice into cultivated rice to date which include genes for resistance to grassy stunt virus, bacterial blight, brown plant hopper, blast (Brar and Khush, 1997). The present study was, therefore, aimed to identify sources of resistant genes to virulent isolates of bacterial blight in wild relatives for future use in rice breeding programs.

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Article source : Resistance Characterization of Cultivated Varieties and Rice Wild Species in Response toBacterial Blight