Phytopathogenic Bacteria and Plant Diseases

BS Thind

• Editorial: CRC Press
• Año: 2019
• ISBN:
  9780429515934
• Edición: 1
• Categoría: Biological Sciences
• Categoría: Botany

The field of Phytobacteriology is rapidly advancing and changing, because of recent advances in genomics and molecular plant pathology, but also due to the global spread of bacterial plant diseases and the emergence of new bacterial diseases. So, there is a need to integrate understanding of bacterial taxonomy, genomics, and basic plant pathology that reflects state-of-the-art knowledge about plant-disease mechanisms. This book describes seventy specific bacterial plant diseases and presents up-to-date classification of plant pathogenic bacteria. It would be of great help for scientists and researchers in conducting research on ongoing projects or formulation of new research projects. The book will also serve as a text book for advanced undergraduate and postgraduate students of disciplines of Phytobacteriology and Plant Pathology.

• Contains latest and updated information of plant pathogenic bacteria till December 2018
• Describes seventy specific bacterial diseases
• Presents classification of the bacteria and associated nomenclature based on Bergey's Manual Systematic Bacteriology and International Journal of Systematic and Evolutionary Microbiology
• Discusses practical and thoroughly tested disease management strategies that would help in controlling enormous losses caused by these plant diseases
• Reviews role of Type I-VI secretion systems and peptide- or protein-containing toxins produced by bacterial plant pathogens
• Briefs about plants and plant products that act as carriers of human enteric bacterial pathogens, like emphasizing role of seed sprouts as a common vehicle in causing food-borne illness

Dr B. S. Thind was ex-Professor-cum-Head, Department of Plant Pathology, Punjab Agricultural University Ludhiana, India. He has 34 years of experience in teaching, research, and transfer of technology. He has conducted research investigations on bacterial blight of rice, bacterial stalk rot of maize, bacterial blight of cowpea, bacterial leaf spot of green gram, bacterial leaf spot of chillies and bacterial soft rot of potatoes. He also acted as Principal Investigator of two ICAR-funded research schemes entitled, "Detection and control of phytopathogenic bacteria from cowpea and mungbean seeds from 1981 to 1986 and "Perpetuation, variability, and control of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight of rice" from 1989 to 1993, and also of a DST funded research scheme "Biological control of bacterial blight, sheath blight, sheath rot, and brown leaf spot of rice" from 1999 to 2002. He also authored a manual entitled, "Plant Bacteriology" and a text book entitled, "Phytopathogenic Procaryotes and Plant Diseases" published by Scientific Publishers (India). He is Life member of Indian Phytopathological Society, Indian Society of Plant Pathologists, Indian Society of Mycology and Plant Pathology, and Indian Science Congress Association.

Section II

Specific Plant Diseases

7	Description of Plant Diseases

7.1 BACTERIAL BLIGHT OF RICE

Bacterial blight (hereafter referred to as BB) is one of the most devastating diseases of rice (Oryza sativa L.) due to its very high epiphytotic potential and its destructiveness to nitrogen-responsive high yielding cultivars in both temperate and tropical climates. Its occurrence in 1970 in Africa has added a new dimension to concerns about its transmission and dissemination. It has also been a serious problem on hybrid rice. In the 1980s when hybrid rice was first released in China, epiphytotics occurred widely because of lack of resistance in the hybrid rice, resulting in severe yield losses.

It is probably one of the most extensively studied diseases and a large number of research publications, dealing with different aspects of the pathogen and the disease, have appeared in the literature. Mew et al. (1993), in their paper “Focus on bacterial blight of rice,” have provided information on various aspects of the pathogen and the disease. Several review papers containing valuable information on the disease have also been published by workers from different countries. Two such review papers have also appeared from India (Srivastava 1972; Thind 2002). The review paper by Nino-Liu et al. (2006) provides very useful information on different aspects of the casual agent of the disease. Khan et al. (2014), in a mini-review, have consolidated the existing information on the disease and the progress made both in conventional as well as in molecular dimensions of breeding together with potential findings and constraints. For additional information, the readers may also see annual reports of International Rice Research Institute, Philippines and Central Rice Research Institute, Cuttack, India.

The disease was first seen by farmers in the Fukuoka Prefecture of Japan in 1884 and was called white withering disease. Originally, it was believed to be caused by acidic soil. In 1908, Takaishi observed bacterial masses in dewdrops of infected rice leaves, successfully isolated a bacterium and proved its pathogenicity, but did not name the organism. Bokura, in 1911, also isolated a bacterium, proved its pathogenicity, and named it Bacillus oryzae Hori & Bokura. Reitsma and Schure (1950) studied a rice disease called Kresek in Indonesia and considering it different from bacterial blight, named the bacterium as Xanthomonas kresek. Later, Goto (1964) reported the pale yellow leaf phase of the disease, which occurs at a later stage of growth. Both kresek phase and pale yellow leaf phase are different phases of bacterial blight.

The disease is widespread and occurs in the Philippines, Thailand, Indonesia, China, Taiwan, Malaysia, Cambodia, Vietnam, Myanmar, Laos, Bangladesh, Mexico, Southeast Russia, Australia, Pakistan, West Africa, Latin America, the Caribbean, and India. However, the presence of the disease has not been confirmed in the United States and not yet found in Europe. Quarantines for BB pathogen are in place in the United States and other rice growing countries where the disease is not endemic, but also in places where it is present, to prevent the introduction of new virulent strains. It is also an European and Mediterranean Plant Protection Organization (EPPO) A1 quarantine pest.

In India, Sreenivasan et al. (1959) reported the disease for the first time from Maharashtra, but the symptoms described by them were not exactly of bacterial blight. Bhapkar et al. (1960) reported correct symptoms of the disease, but they did not isolate the bacterium. Later, Srivastava and Rao (1963) reported its epiphytotic on cv. BR 34 from Shahabad district of Bihar. During this period, a Formosian rice variety, Taichung Native 1, a high nitrogen-responsive, but resistant to lodging was introduced into India to step up the rice production. As this variety was highly susceptible to the disease, the disease that was unknown in all but two states of India earlier, became pandemic within a couple of years with the introduction of this variety.

Although the disease occurs in many countries, it is most destructive in Southeast Asia. The yield losses vary with host cultivar, age, and nutrition of the host and environmental conditions. They are usually high in early infected crop, and the occurrence of kresek phase may lead to total failure of the crop in some cases. Losses due to BB increased significantly following the widespread cultivation of nitrogen-responsive, high yielding, semi-dwarf rice cultivars derived from Taichung Native 1 and its derivatives in the 1960s. Prior to the introduction of resistant varieties and implementation of strict quarantine measures in Japan, losses generally ranged from 20% to 30%, but in some cases went as high as 50% (Ou 1972). Reports from India, the Philippines, and Indonesia estimate that losses due to kresek phase have reached 60%–75% depending on weather, location, and rice variety (Reddy et al. 1979a; Ou 1985). Ray and Sengupta (1970) also reported losses up to 50% from semi-dwarf high yielding varieties. Singh et al. (1977) reported that four rice cultivars with a similar leaf score of 9 showed variable loss in grain yield. Reddy et al. (1979b) established a relationship between severity of BB at different growth stages of host plant and rice yield and found that early epiphytotics reduced grain yield, panicle fertility, and kernel weight, while late epiphytotics had no measurable effect on crop yield. They also devised a scale for calculating BB-associated losses. In addition to reduction in yield, the disease may also affect grain quality by interfering with maturation.

7.1.1 SYMPTOMS

It is a typical vascular disease. The below given three different types of symptoms appear.

7.1.1.1 Leaf Blight Phase

These are the most common symptoms of the disease and generally appear 4–6 weeks after transplanting. Initially, the symptoms start as small, green, water-soaked spots at the tips and margins of fully developed leaves. The spots extend forming linear, yellow- to straw-colored stripes having wavy inner margins. The stripes appear generally on both the margins and rarely on one margin of the leaves. The stripes progress rapidly, extending lengthwise and crosswise. The drying and twisting of the leaf tips occur (Figure 7.1a). Occasionally, linear stripes may develop anywhere on the leaf lamina or midrib with or without marginal stripes. The blightening extends to leaf sheaths, culms, killing the tillers. In humid weather, yellow- or amber-colored drops of bacterial ooze appear on young lesions at the margins of the leaves. On drying, these drops form yellowish hard beads. The symptoms on panicles appear as grey to light brown lesions on glumes, resulting in poor fertility and low quality grains. The symptoms of BB often occur simultaneously with those of bacterial leaf streak, and individual leaves may show symptoms of both the diseases.

7.1.1.2 Kresek (Wilt) Phase

It is the most destructive phase of the disease and results from systemic infection of plants in the nursery or early infection in the main field. In an infected plant, the bacteria spread through xylem of the infected leaf to the culm and infect the crown (base of other leaves). Subsequently, all the tillers of the plants are infected resulting in quick wilting of the entire plant. The leaves of the affected plants roll completely, droop, and turn yellow or grey. Ultimately, the diseased tillers wither away and in severely infected plants, stools are killed. The plants that survive, exhibit arrested growth of tillers and stunted appearance (Figure 7.1b). Kresek phase is common in tropical countries. Temperature range of 28°C–34°C favors kresek development. Kresek phase is generally confused with stem borer attack. However, in the latter case, affected tillers/panicles can be easily pulled out and detached part of the tiller shows the signs of insect feeding at the broken end.

FIGURE 7.1 Bacterial blight of rice: (a) Leaf blight phase. (b) Kresek phase.

7.1.1.3 Pale Yellow Leaf Phase

The youngest leaves in a clump turn pale yellow or whitish. The diseased leaves later turn yellowish brown and tillers do not grow fully.

The disease can be easily diagnosed in the field on the basis of symptoms described above. Additionally, the field diagnosis of the disease can be supplemented by placing infected leaf bits in a glass of clean water. If the water turns turbid after some time, presence of the disease is confirmed. However, further confirmation of the diagnosis can be done by observing the bacterial ooze in the laboratory.

Symptoms of bacterial blight on rice leaves, characteristics to those caused by Xa. oryzae pv. oryzae, have been reported to be caused by Pantoea ananatis and Pa. stewartii in Togo (Kini et al. 2017).

7.1.2 CAUSAL ORGANISM

Xanthomonas oryzae pv. oryzae (Ishiyama 1922) Swings et al. 1990

Syn. Xa. oryzae, Xa. campestris pv. oryzae

The bacterium was first named as Bacillus oryzae Hori & Bokura. Ishiyama (1922) renamed it as Pseudomonas oryzae Uyeda & Ishiyama according to Migula’s system of classification. In 1927, it was renamed as Bacterium oryzae (Uyeda & Ishiyama) Nakata according to E.F. Smith’s concept and subsequently to Xanthomonas oryzae (Uyeda & Ishiyama) Dowson with the creation of Xanthomonas genus. With the introduction of pathovar concept, the name Xa. campestris pv. oryzae (Ishiyama) Dye was adopted (Dye 1978). Swings et al. (1990), on the basis of phenotypic, genotypic, and chemotaxonomic data, proposed Xanthomonas oryzae (ex Ishiyama 1922) sp. nov., nom. rev. and renamed the blight pathogen as Xanthomonas oryzae pv. oryzae (Ishiyama) Swings et al. (hereafter referred to as Xoo). The following description of Xa. oryzae (ex Ishiyama 1922) sp. nov., nom. rev. is taken primarily from Swings et al. (1990).

Cells are straight rods (0.4–0.8 × 1.5–2.9 µm) having round ends, Gram-stain-negative, non-sporulating, and motile with a single polar flagellum. Cells occur singly, in pairs, or sometimes in chains and filaments may also occur. The bacterium is obligately aerobic and catalase positive. Colonies on solid media containing glucose are round, convex, mucoid, and yellow in color due to production of xanthomonadin. Xanthomonadin, though not required for virulence, protects the bacterium form UV light and probably contributes to its survival in the field. The cells produce copious, capsular extracellular polysaccharide (EPS). EPS plays a role in virulence, and Xoo mutants lacking this ability are severely attenuated in virulence. The tests for indole and 2-ketogluconate formation, urease, egg yolk hydrolysis, nitrate reduction, and oxidase are negative. Starch is hydrolyzed and carbon sources are used only oxidatively. Litmus milk is not acidified, but H₂S is produced. Esculin, Tween 40, and 80 are hydrolyzed. No growth occurs at 4°C or 35°C or in the presence of 3% NaCl, but poor growth occurs at 10°C and 32°C. Optimum temperature for growth is between 25°C and 30°C. The G + C contents of the DNA range from 64.6 to 65.0 mol%.

Xoo differs from Xa. oryzae pv. oryzicola in causing different type of symptoms on rice. Xoo also differs from pathovar oryzicola in not producing acetoin, inability to use L-alanine as sole source of carbon, and unable to grow on 0.2% vitamin-free casamino acids. However, Xa. oryzae pv. oryzicola is positive for all the above given three characteristics. Xoo is able to grow in the presence of 0.001% cupric nitrate, while Xa. oryzae pv. oryzicola is not.

Xu et al. (2010) obtained 534 single-colony isolates of Xoo from rice leaves showing bacterial blight symptoms, collected from southern China in 2007 and 2008 and tested these isolates on plates for sensitivity to streptomycin. Four strains (0.75%)...