Cassava Bacterial Blight in Uganda

Abstract

Cassava bacterial blight (CBB) is a major problem of cassava in Uganda. It was first recorded in Terego County, Nile Province in 1976, and a disease survey indicated that CBB is now present in over half of the country. Losses of 90–100% have been observed on susceptible varieties in parts of the Nile, North and Eastern provinces. Symptoms include angular leaf spots, blight, wilt dieback and gum exudations. Planting of infected materials, rainfall, hailstorms, wind and insects are major factors in the spread of the disease. Restriction of movement of infected cassava cuttings to non-infected areas, planting of resistant varieties and healthy cuttings, encouragement of mixed cropping and crop rotation are recommended for control.     

Screening for Resistance to Bacterial Blight in Cowpea

Abstract

The evaluation of greenhouse and field screening methods for the identification of resistance to bacterial blight (Xanthomonas vignicola Burkh.) amongst germplasm and breeding lines of cowpea (Vigna unguiculata(L.) Walp.) is described. A stem injection technique and a leaf infiltration method were found reliable under greenhouse conditions while foliar spray inoculation was appropriate for use in both greenhouse and field experiments. A seed inoculation technique for evaluating seedling mortality may prove useful although only one susceptible cowpea accession was used in this study. Since distinct syndromes of bacterial blight (seedling mortality, stem canker and foliar blight) are recognised, it may be advantageous to adopt a different inoculation method for each syndrome to establish the relationship between the resistance of different plant parts within cowpea genotypes. Results confirm the existence of at least two distinct mechanisms of resistance to bacterial blight in cowpea. Hypersensitive resistance was clearly demonstrated in the accession TVu 410 by the leaf injection infiltration method; VITA 3 was shown to possess a field resistance, expressed as reduced and delayed disease development. The probable stability of these mechanisms is discussed with regard to their suitability as breeding objectives.     

水稻对白叶枯病抗性基因的研究进展

概述了水稻抗白叶枯病的机制及抗性基因的研究进展、基因工程育种等。     

Harpin xoo在水稻中表达提高对白叶枯病不同小种抗性

用剪叶接种法测定10个转hrf1基因水稻株系对15个水稻白叶枯病菌小种的抗性.所有的转基因系对JxOV和PXO79小种的抗性与受体对照相比显著提高,RT-PCR结果显示,在转化hrf1基因的抗病水稻中,信号传导基因npr1表达明显增强,表明转hrf1基因水稻可能通过激发水稻中信号传导基因的表达,提高对白叶枯病菌不同小种的抗性.     

Identification of Pathotypes of Xanthomonas axonopodis pv. manihotis in Africa and Detection of Quantitative Trait Loci and Markers for Resistance to Bacterial Blight of Cassava

ABSTRACT Cassava suffers from bacterial blight attack in all growing regions. Control by resistance is unstable due to high genotype-environment interactions. Identifying genes for resistance to African strains of Xanthomonas axonopodis pv. manihotis can support breeding efforts. Five F(1) cassava genotypes deriving from the male parent 'CM2177-2' and the female parent 'TMS30572' were used to produce 111 individuals by backcrossing to the female parent. In all, 16 genotypes among the mapping population were resistant to stem inoculation by four strains of X. axonopodis pv. manihotis from different locations in Africa, and 19 groups with differential reactions to the four strains were identified, suggesting that the strains represent different pathotypes. Four genotypes were resistant to leaf inoculation, and three were resistant to both stem and leaf inoculations. Genotypes with susceptible, moderately resistant, and resistant reactions after leaf and stem inoculation partly differed in their reactions on leaves and stems. Based on the genetic map of cassava, single-markeranalysis of disease severity after stem-puncture inoculation was performed. Eleven markers were identified, explaining between 16 and 33.3% of phenotypic variance of area under disease progress curve. Five markers on three and one linkage groups from the female- and male-derived framework of family CM8820, respectively, seem to be weakly associated with resistance to four strains of X. axonopodis pv. manihotis. Based on the segregation of alleles from the female of family CM8873, one marker was significantly associated with resistance to two X. axonopodis pv. manihotis strains, GSPB2506 and GSPB2511, whereas five markers were not linked to any linkage group. The quantitative trait loci (QTL) mapping results also suggest that the four African strains belong to four different pathotypes. The identified pathotypes should be useful for screening for resistance, and the QTL and markers will support breeding for resistance.     

Identification of Resistance to Common Bacterial Blight Disease on Bean Genotypes Grown in Turkey

Common bacterial blight (CBB) in edible beans (Phaseolus vulgaris), incited Xanthomonas campestris pv. phaseoli, reduces bean yields and seed quality. The main objective of this study was to determine resistance to common bacterial blight in bean genotypes. Twenty-two bean genotypes grown in Turkey including common and snap bean cultivars/lines were collected from different parts of Turkey and tested for resistance against to Xanthomonas campestris pv. phaseoli strain MFD-11. All the common and snap bean lines/cultivars tested were moderately susceptible, susceptible or highly susceptible, except AG-7117 which was found resistant to Xanthomonas campestris pv. phaseoli. This is the first report of a resistance source in a common bean line (AG-7117) against Xanthomonas campestris pv. phaseoli.     

Localizing the Bacterial Blight Resistance Gene, Xa22(t), to a 100-Kilobase Bacterial Artificial Chromosome

ABSTRACT The rice bacterial blight resistance gene, Xa22(t), provides resistance to a broad spectrum of Xanthomonas oryzae pv. oryzae isolates. Here, we localize the gene to a small 100-kb fragment of chromosome 11 by a combination of genetic recombination analysis and physical mapping. Mapping was done with two F(2) populations from the cross between Zhachanglong and Zhenzhuai. The first population consisted of 248 random individuals and 404 highly susceptible individuals selected from an F(2) population of more than 2,000 individuals and was used to construct a linkage map around the Xa22(t) locus. For the second F(2) population, 7,680 plants were examined with simple sequence repeat markers flanking the Xa22(t) locus to identify recombinants useful for fine-genetic mapping. Two large-insert bacterial artificial chromasome (BAC) libraries (from cvs. Teqing and Minghui63) were screened with a marker (R1506) which cosegregated perfectly with Xa22(t) in the first population. Restriction mapping of the resulting BAC clones enabled a physical map of the area to be constructed, and subclones from the BAC clones provided additional restriction fragment length polymorphism probes which could be placed on the fine-structure genetic map using the recombinants from the second mapping population. The Xa22(t) locus was mapped to a approximately 100-kb interval delimited by the R1506 marker and a subclone from the M3H8 BAC clone.     

Bacterial Diseases of Cassava

Abstract

Recent developments on the identities of the causal agents of bacterial diseases of cassava throughout the world are discussed.     

Genotype × environment Effects on Severity of Cassava Bacterial Blight Disease caused by Xanthomonas axonopodis pv. manihotis

Nine cassava genotypes were grown for three years at six sites representing three agro-ecological zones in Nigeria to study their reaction to cassava bacterial blight (CBB), investigate genotype × environment (G × E) interaction patterns for their reaction to CBB, and to identify genotypes with stability to the disease, using the additive main effects and multiplicative interaction (AMMI) statistical model. Environments, genotypes and G × E interactions accounted for 71.8%, 12.0% and 16.2% of the treatment sums of squares (SS), and were highly significant (P<0.0001) for the disease, indicating that genotypes responded differentially to CBB infection across environments. Clones 30555, 91934, U/41044, and 4(2)1425 showed the least CBB disease ratings. Other clones showed erratic and fluctuating reactions to CBB from environment to environment and were thus considered unstable to the disease. CBB was most severe in 1989 (with a mean score of 2.46) and least so in 1990 (with a score of 2.06). The sites with the most disease were Ibadan, Ilorin and Ubiaja (1989), Ibadan and Ubiaja (1990) and Mokwa (1991). Because of the favourable conditions for disease development at those sites, they could be appropriate for screening cassava genotypes for CBB resistance. The AMMI model selected AMMI1 as the best predictor for CBB because it had the smallest actual root mean square prediction difference (0.37646), and explained 90.7% of the G × E interaction for CBB. The AMMI model was successful in selecting the genotypes 30555, U/41044 and 4(2)1425 and the environments Ibadan 1989, Ilorin 1989 and Onne 1990 with stability of reaction to the disease.     

Bacterial Blight of Cotton in Sudan

Abstract

This paper is in effect a summary of three COPR reports (Pope, 1973 and 1974, Pope and Watt, 1975) which is intended to give the reader an indication of possible uses for light hovercraft under field conditions both in the United Kingdom and overseas. Some suggestions are made as to possible uses and various forms of equipment and modifications are described and discussed.     

Dynamics of Xanthomonas oryzae pv. oryzae Populations in Korea and Their Relationship to Known Bacterial Blight Resistance Genes

ABSTRACT Developing resistant cultivars requires an understanding of the dynamics of the pathogen populations as well as the genetics of host resistance. Bacterial leaf blight (BB), caused by the vascular pathogen Xanthomonas oryzae pv. oryzae, has become one of the most devastating diseases of rice. We demonstrate here the quantitative analyses of responses of near-isogenic lines carrying various BB resistance (R) genes and R-gene combinations against 16 X. oryzae pv. oryzae isolates representing Korean BB pathotypes. The estimated main effects of each R gene against the 16 isolates identified prominent differences in BB pathotypes between Korea and other countries. Three major aspects of our quantitative observations and statistical analysis are (i) strong and broad resistance of xa5; (ii) independent and additive genetic actions of Xa4, xa5, and Xa21 under digenic or trigenic status; and (iii) a strong quantitative complementation effect contributed by the functional alleles of Xa4 and Xa21. We conclude that the pyramid line containing genes Xa4, xa5, and Xa21 would be the most promising and valuable genotype for improving Korean japonica cultivars for BB resistance.     

Bacterial Blight Disease of Rice in India

Abstract

A Mycosphaerella sp. distinct from Mycosphaerella musicola Leach has been found in a banana plantation in Zambia and has caused severe losses in the 1973–1974 season.     

The Components and Deployment of Resistance to Cassava Mosaic Virus Disease

Cassava mosaic virus disease (CMD) is prevalent and causes serious losses in cassava (Manihot esculenta) in southern India and in many parts of sub-Saharan Africa. The disease is caused by viruses of the Geminiviridae that are transmitted by the whitefly Bemisia tabaci and disseminated in the stem cuttings used routinely for propagation. The main approach to control is through the use of virus-resistant varieties, but suitable ones are not always available and susceptible varieties are still widely grown. This explains why CMD continues to be a problem in many areas.CMD-resistant varieties have several features which are considered in this review:- They are not readily infected, even when exposed to large amounts of vector-borne inoculum. When infected they develop symptoms that tend to be inconspicuous and not associated with obvious deleterious effects on growth or yield. Moreover, the symptoms become even less conspicuous as growth proceeds and plants may eventually recover and become symptomless. Infected plants support a low virus content and they are likely to be a poor source of inoculum from which further spread can occur. Virus is not fully systemic within infected plants which can be a source of uninfected planting material when stem cuttings are collected for further propagation. This phenomenon is referred to as reversion and it has an important cleansing effect in restricting or preventing the progressive deterioration in health status that would otherwise occur during successive cycles of vegetative propagation.The available information on the different components of resistance is discussed and it is concluded that they are inter-related features of the same basic mechanism that restricts virus entry, replication and movement within the host. It is argued that the effectiveness and durability of virus-resistant varieties are likely to be influenced by the way in which they are deployed. However, this topic has received little attention from researchers and there is continuing uncertainty on the effects of CMD on the yield of resistant varieties and on the role of phytosanitation. This involves the use of virus-free planting material and the removal (roguing) of any additional diseased plants that occur. Some consider that these procedures complement the use of virus-resistant varieties and should be adopted, whereas others argue that they are unnecessary and inappropriate. It is concluded that there is considerable scope for utilizing resistant varieties more widely and more effectively than at present, but in doing so it is important to avoid eroding the genetic diversity that is currently such a marked feature of cassava cultivation in Africa.     

Genetic Analysis of the Relationship between the Browning Reaction and Bacterial Blight Resistance Gene Xa3 in Rice

The relationship between bacterial blight resistance gene Xa3 and browning reaction was genetically analyzed using F₂ plants from the cross of rice cultivar Kuntulan with Kinmaze. Kuntulan harbors resistance Xa3 and developes a browning reaction to avirulent races of Xanthomonas oryzae pv. oryzae, whereas Kinmaze has a typical susceptible reaction to all known Japanese races of X. o. pv. oryzae. The F₂ plants were tested for their resistance to avirulent race II strain of X. o. pv. oryzae and the development of browning. Of 337 F₂ plants tested, 251 had resistance to the strain. In all the resistant plants, a browning reaction developed around the point of inoculation. The remaining 86 had a susceptible reaction to the strain without a browning reaction. The F₂ population of Kuntulan × Kinmaze had a clear-cut segregation ratio of 3R : 1S. These facts led to the conclusion that the browning reaction is a pleiotropic effect of Xa3. Received 29 January 2001/ Accepted in revised form 24 April 2001     

我国水稻纹枯病拮抗细菌种类研究

1996～2002年间从浙江、江苏、福建和云南等稻区采集稻种和稻株样本921份，从中分离出11635个细菌菌株，用平板对峙培养法进行了对水稻纹枯病菌的拮抗测试。经致病性测定、菌落形态及部分细菌学特征测定后，选出代表菌株631个连同26个对照菌株用Biolog及脂肪酸分析法进行测试。鉴定出假单胞菌属11个种或型，其中8个种内测到拮抗菌株，平均抑菌率为24．3％；其他非致病细菌14属的25种中13个种内存在拮抗菌，平均抑菌率为14．3％，明显低于假单胞菌属。     

Resistance and Resistance Breeding in Ornamentals 1

Heritability studies in ornamentals with regard to Erwinia amylovora (Burrill) Winslow et al. were started shortly after the introduction of the pathogen into northern Europe. Since that time, approximately 8,000 plants from 17 genera of Rosaceae have been tested; 7 genera were reported to be susceptible: the economically important Cotoneaster, Crataegus, Cydonia, Pyracantha, Sorbus, and, in addition, Chaenomeles and Stranvaesia. Moreover, 9,000 Cotoneaster seedlings comprising 15 cultivars were tested and the surviving individuals used for breeding purposes. The variation between these first results reported in the different European countries and some American findings is considerable because of different inoculation procedures and various epidemiological conditions. However, resistance sources have been identified and it would be desirable to start co–operation in this field on an international level.     

部分马铃薯主栽品种对晚疫病的田间抗性研究

为摸清贵州省低海拔地区主栽马铃薯品种对晚疫病的抗性情况,2012年对贵州省13个主栽马铃薯品种进行晚疫病抗性鉴定试验。结果表明：Z-30、BP05-003（产量在25500kg／hm2以上）对晚疫病表现为中感,为早、中熟品种,适宜在低海拔发病不重的区域推广;滇黔芋2号、米拉（产量在13500kg／hm2以上）对晚疫病表现为感病,如在晚疫病常发区、重发区种植,生产上应加大防治力度;BPHFl01、20-4．5、威薯002为中感及感病品种,产量一般,为晚熟品种,适宜在高海拔地区种植,需要加强晚疫病防治并配套高产栽培技术。     

Phylogenetic and Pathotypic Analysis of Rice Bacterial Blight Race 3

Eight Philippine races of Xanthomonas oryzae pv. oryzae have been identified based on virulence phenotypes observed on a set of five differential varieties. One of these, Race 3, was found to consist of two phylogenetically distinct lineages based on DNA fingerprinting analysis. To determine, if the two lineages could be differentiated based on host-specificity, 186 strains of Race 3 were analyzed with additional fingerprints and 76 selected isolates with additional differential rice varieties. The strains were separated into 36 haplotypes clustering in three groups (IS1113-B, -C, and -G) at the 75% similarity level. Isolates varied in their reaction to a rice line carrying the resistance gene Xa7, however, the variability was not consistent within lineage. Aggressiveness of isolates belonging to lineage IS1113-B and -G was significantly greater when tested during the dry season than when tested during the wet season. However, no such differences were evident for isolates from lineage IS1113-C, indicating that environmental effects presumably light and temperature are genotype-specific.