Asian Vegetable Research Research Articles

Comportamento de linhagens de feijão-mungo(Vigna radiata L.) em Santa Catarina

Foram conduzidos três experimentos na fazenda experimental do Centro de Ciências Agrárias da Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil. A finalidade do trabalho foi avaliar o comportamento de 29 linhagens de feijão mungo provenientes do "Asian Vegetable Research and Development Center" (AVRDC). Avaliaram-se as características agronômicas (formacão da primeira flor, primeiro legume maduro, estatura da planta), o peso de mil sementes e o rendimento. As linhagens foram testadas em blocos ao acaso, com quatro repetições. Cada parcela foi constituída por 4 linhas de 6m de comprimento, espaçadas de 50cm, com vinte sementes por metro de sulco. A floração inicial das linhagens ocorreu entre os 33 e 49 dias após o plantio, enquanto a maturação do primeiro legume se deu entre os 70 e 78 dias após a semeadura. A estatura das plantas e o peso de mil sementes variaram entre 22,5 e 63,8cm e 33,0 e 76,4g respectivamente. As linhagens mais produtivas foram: VC 3890B, VC 1973C e VC 2764B com rendimento acima de 1140kg.ha-1. Estas linhagens apresentaram peso de mil sementes e estatura de planta boas para cultivo e um ciclo biológico médio. A colheita foi feita em uma única operação, entre 80 e 85 dias após a semeadura no primeiro e segundo experimentos. No terceiro experimento, a colheita foi feita em duas vezes, aos 80 e 85 dias e aos 95 e 100 dias, sendo que na primeira colheita foram colhidos 78% dos legumes; os restantes 22% foram colhidos 15 dias após a primeira.

Evaluation of Onion Cultivars for Resistance to Aspergillus niger, the Causal Agent of Black Mold

Black mold (BM), caused by Aspergillus niger Tiegh., is a common onion (Allium cepa L.) postharvest disease under hot and humid storage conditions. This study aimed to develop a BM screening protocol, to evaluate onion cultivars for resistance. The effects of pathogen isolate, inoculum density, incubation temperature, and inoculation method on severity of BM were investigated in designing the screening protocol. Variation in virulence was observed and two highly virulent subcultures, An4-2 and An39-3, were selected for study. Disease severity, both in lesion size and sporulation degree, increased with higher inoculum densities and incubation temperatures. In contrast, small lesions and no sporulation were observed when onion scales were inoculated with 1 × 104 spores/mL or incubated at temperatures lower than 20 °C. Inoculation of onion scales or entire bulbs were compared and scale inoculation correlated better with BM incidence in storage. The procedure for BM screening protocol included: wound inoculation of onion slices with 40 μL inoculum suspension of 1 × 105 spores/mL, incubation at 25 °C with 12 hour photoperiod, and rating lesion diameter and sporulation 4 days after inoculation. Using this screening protocol, 42 onion cultivars were evaluated and cultivars with better storability such as `Red Pinoy', `Serrana', `Dehydrator No.3', and `Moonlight' were tolerant to A. niger. These cultivars showed small lesions and no sporulation during screening. On the other hand, cultivars with poor storability like `Texas Early Grano 502', `Granex 429', and `Explorer' exhibited larger lesions with profuse sporulation. Lesion diameter caused by the scale inoculation correlated significantly with bulb storage loss (r = 0.51, P < 0.01) as well as with bulb dry matter (r = -0.48, P < 0.01) and total soluble solids (r = - 0.51, P < 0.01). The screening protocol and tolerant materials are now successfully used in the Asian Vegetable Research and Development Center onion breeding program for resistance to black mold.

Ouro Verde MG 2: nova cultivar de mungo-verde para Minas Gerais

Dentre várias linhagens introduzidas do "Asian Vegetable Research and Development Center" (AVRDC), sobressaiu a linhagem VC 3984-B-2-B-4-1-B, que recebeu o nome de Ouro Verde MG 2. Suas sementes são verde-brilhantes e o peso de 1000 unidades varia de 43 a 51 g. O início da floração ocorre em torno de 33 dias após a emergência e a primeira vagem madura surge entre 23 e 33 dias. Por se tratar de espécie de maturação desuniforme, podem ser necessárias duas a quatro colheitas. As plantas podem atingir 95 cm de altura. As vagens são marrom-escuras e concentram-se na parte superior da planta. É suscetível a duas doenças que geralmente aparecem no final do ciclo de vida do mungo-verde: míldio-pulverulento (Erysiphe polygoni) e mancha-foliar-de-cercospora (Cercospora canescens). A 'Ouro Verde MG 2' é resistente ao acamamento, e o seu rendimento, em três ensaios instalados em dezembro, janeiro e fevereiro, variou de 1,5 a 2,0 t/ha. Esses rendimentos foram, em média, 12% superior ao da cultivar Ouro Verde.

Gene Action and Heritability of High-temperature Fruit Set in Tomato Line CL5915

High-temperature fruit set (heat tolerance) is a critical trait of tomato (Lycopersicon esculentum Mill.) cultivars targeted for lowland wet season production in the tropics and subtropics. Heat-tolerant Asian Vegetable Research and Development Center (AVRDC) tomato line CL5915-93D4-1-0-3 (CL5915) is a valuable source of heat-tolerance genes for tomato genetic improvement. The gene action of heat tolerance in CL5915 was determined by evaluating the F1, F2, BCP1, and BCP2 of a cross between CL5915 and heat-sensitive line UC204A for fruit set traits in two wet-season trials at AVRDC. Parent-offspring regression of F2-derived F3 (F2:3) family means on the F2 plants from CL5915 × UC204A was used to estimate the heritability of F2 single plant selection for heat tolerance. Mean percentage of fruit set and fruit number per cluster of the F1 and BCP1 exceeded midparent values and were not significantly different from those of CL5915, indicating complete dominance for heat tolerance. Generation means analyses indicated that a model including simple additive and dominance effects adequately explained the inheritance of mean fruit number per cluster both years. For mean percentage of fruit set, a model including simple additive-dominance effects produced an adequately fitting model in the 1996 season but the best-fitting model included an epistatic component in the 1997 season. Heritabilities estimated for fruit set traits in 1996 and 1997, respectively, were: 0.31 and 0.21 for percentage of fruit set; 0.28 and 0.14 for mean fruit number per cluster; and 0.53 and 0.15 for flower number per cluster. The low heritabilities for percentage of fruit set and mean fruit number per cluster under high temperatures imply that single plant selection in the F2 for heat tolerance from crosses involving CL5915 is not effective and that selection should be based on replicated family testing in the F3 and later generations.

Molecular Characterization of Begomoviruses Associated with Leafcurl Diseases of Tomato in Bangladesh, Laos, Malaysia, Myanmar, and Vietnam.

Production of tomato (Lycopersicon esculentum) in Bangladesh, Malaysia, Myanmar, Vietnam, and Laos has been severely affected by yellow leaf curl disease. Tomato leaf samples were collected from symptomatic tomato plants from farmers' fields in the five countries from 1997 to 1999. DNA was extracted from all samples, four from Vietnam, two each from Malaysia, Laos, and Myanmar, and seven from Bangladesh. Virus DNA was amplified by polymerase chain reaction (PCR) using the begomovirus-specific degenerate primer pair PAL1v 1978/PAR1c 715(1), which amplifies the top part of DNA A. All samples gave the expected 1.4-kb PCR product. The PCR product of one sample per country was cloned and sequenced. Based on the sequences of the 1.4-kb DNA products amplified by the first primer pair, specific primers were designed to complete each of the DNA A sequences. Computer-assisted sequence comparisons were performed with begomovirus sequences available in the laboratory at the Asian Vegetable Research and Development Center, Shanhua, Tainan, and in the GenBank sequence database. The five DNA species resembled DNA A of begomoviruses. For the detection of DNA B two degenerate primer pairs were used, DNABLC1/DNABLV2 and DNABLC2/DNABLV2 (DNABLC1: 5'-GTVAATGGRGTDCACTTCTG-3', DNABLC2: 5'-RGTDCACTT CTGYARGATGC-3', DNABLV2: 5'-GAGTAGTAGTGBAKGTTGCA-3'), which were specifically designed to amplify DNA B of Asian tomato geminiviruses. Only the virus associated with yellow leaf curl of tomato in Bangladesh was found to contain a DNA B component, which was detected with the DNABLC1/DNABLV2 primer pair. The DNA A sequence derived from the virus associated with tomato yellow leaf curl from Myanmar (GenBank Accession No. AF206674) showed highest sequence identity (94%) with tomato yellow leaf curl virus from Thailand (GenBank Accession No. X63015), suggesting that it is a closely related strain of this virus. The other four viruses were distinct begomoviruses, because their sequences shared less than 90% identity with known begomoviruses of tomato or other crops. The sequence derived from the virus associated with tomato yellow leaf curl from Vietnam (GenBank Accession No. AF264063) showed highest sequence identity (82%) with the virus associated with chili leaf curl from Malaysia (GenBank Accession No. AF414287), whereas the virus associated with yellow leaf curl symptoms in tomato in Bangladesh (GenBank Accession No. AF188481) had the highest sequence identity (88%) with a tobacco geminivirus from Yunnan, China (GenBank Accession No. AF240675). The sequence derived from the virus associated with tomato yellow leaf curl from Laos (GenBank Accession No. AF195782) had the highest sequence identity (88%) with the tomato begomovirus from Malaysia (GenBank Accession No. AF327436). This report provides further evidence of the great genetic diversity of tomato-infecting begomoviruses in Asia. Reference: M. R. Rojas et al. Plant Dis. 77:340, 1993.

Uji Adaptasi Somaklonal Kentang (Solanum tuberosum L.) Kultivar Introduksi

One of The Asian Vegetable Research and Development Center programs is to get superior varieties potato. The experiment was objected to study somaclonal variety of several introduced potato varieties in order to select superior varieties from them. The plant height, the number of node, and petiole length of Atlantic cultivar were significant different from somaclonal cultivars, even though the number of stem and internode length were not different. However the number and weight of tuber Red Pontiac, Desiree, Russet Burbank, and Eba significant different from those somaclonal cultivars, but not the Atlantic cultivar. According to the principal component analysis for seven quantitative variables of the 34 plants numbers, there were two principal variables. The both variables I.e. variable 1 and 2, were able to explain about 79.3 % of the total variation. Therefore using the first and second variables may be explained the most of data variation. Somaclonal variation induced by irradiation were able to improve morfologis characters and yield, especially for Atlantic cultivar. Each of Atlantic and Red Pontiac somaclonal cultivar number had far relationship with their mother plants. Key words: Somaclonal, Potato

552 Comparison of Genetic Diversity in between Two Germplasm Banks Containing Lycopersicon esculentum Accessions

Worldwide, there are cuurently more than 60 germplasm banks that contain tomato (Lycopersicon esculentum) collections ranging is size from a few dozen to several thousands of accessions. In the utilization of these genetic resources sampling from only one germplasm bank may result in limiting available genetic diversity, whereas sampling from several germplasm banks may result in unnecessary redundancy. The current lack of knowledge regarding the relative magnitudes of genetic diversity contained within different collections makes it difficult to develop a core collection that maximizes genetic diversity. Two large tomato collections are housed at the Asian Vegetable Research and Development Center (AVRDC), Sanhua, Taiwan, R.O.C., and the Centro Agronomico Tropical de Investigacion y Enseoanza (CATIE), Turrialba, Costa Rica. Ninety-six accessions from CATIE and 102 accessions from AVRDC were randomly sampled from each base collection. The total of 198 accessions were charcterized for 103 polymorphic RAPD molecular marker bands. The results indicated that the two germplam banks sampled different genetic diversity. In addition, the magnitude of genetic diversity was greater in the AVRDC collection compared to CATIE.

Mapping a Wild Tomato Introgression Associated with Tomato Yellow Leaf Curl Virus Resistance in a Cultivated Tomato Line

Tomato yellow leaf curl virus (TYLCV), a heterogeneous complex of whitefly-vectored geminiviruses, is a serious production constraint of tomato (Lycopersicon esculentum Mill.) in Asia, the Middle East, and the Americas. In this study we report on mapping of a DNA fragment introgressed into cultivated tomato presumably from the wild species L. hirsutum Humb. and Bonpl. and found to be associated with TYLCV resistance. To locate introgressions of wild tomato alleles in TYLCV-resistant tomato line H24, its DNA was digested with six restriction enzymes and probed with 90 RFLP markers evenly spaced throughout the genome. This polymorphism survey revealed the presence of one wild tomato introgression each on chromosomes 8 and 11. Plants of a F2 cross between H24 and a susceptible tomato line were probed with randomly amplified polymorphic DNA (RFLP) markers linked to the targeted regions and F3 families were developed by self-pollination of F2 plants that carried none, one, or both introgressions in either homozygous or heterozygous states. Plants of F3 families, parents, and control tomato line Ty52 (homozygous for the Ty-1 allele for TYLCV tolerance) were exposed to viruliferous whiteflies (Bemisia tabaci Gennadius) in greenhouses at the Asian Vegetable Research and Development Center, Taiwan, and the University of Agricultural Sciences, Bangalore, India. Results indicated that F3 families homozygous for the introgression on chromosome 11 were resistant to TYLCV at both locations. Additional probing showed that the chromosome 11 introgression spanned markers TG36 to TG393, covering a distance of at least 14.6 centimorgans. This is the first report of TYLCV resistance in tomato mapped to chromosome 11.

The Integrated Research Approach of the Asian Vegetable Research and Development Center (AVRDC) to Enhance Micronutrient Availability

This paper describes various activities of the Asian Vegetable Research and Development Center (AVRDC) in enhancing micronutrient availability through increased vegetable supply, improved micronutrient density in vegetables, enhanced micronutrient bioavailability, and recommendations for programmes and policies generated through economic research. Technological, nutritional, and socio-economic research are integrated at AVRDC. Nutrient considerations are incorporated at all levels of research planning, technology development, and dissemination of these technologies to clients. The approach ensures not only greater diversity and improved palatability of food, but also enhanced income and employment to poor farming and landless households and improved gender equity. All these factors are catalysts to improved health as well as faster economic growth for developing economies. To tackle widespread micronutrient deficiencies, future nutritional research should focus on making improved vegetable technologies economically viable under a wider range of economic and ecological environments, while enhancing or, at minimum, maintaining the nutrient density and bioavailability of new vegetable releases. To improve the efficiency of nutritional research, the dollar value of micronutrient enhancement research needs to be quantified and compared for different vegetables and other food items. A methodology for doing this is proposed and illustrated.

Variation among and within Capsicum species revealed by RAPD markers

Germplasm characterization is an important link between the conservation and utilization of plant genetic resources. A total of 134 accessions from six Capsicumspecies maintained at the Asian Vegetable Research and Development Center were characterized using 110 randomly amplified polymorphic DNA (RAPD) markers. Ten pairs of potentially duplicated accessions were identified. Multidimensional scaling analysis of the genetic distances among accessions resulted in clustering corresponding to a previous species assignment except for six accessions. Diagnostic RAPDs were identified which discriminate among the Capsicumspecies. The diagnostic markers were employed for improved taxonomic identification of accessions since many morphological traits used in the identification of Capsicumare difficult to score. Three Capsicumaccessions, misclassified based on morphological traits, were reassigned species status based on diagnostic RAPDs. Three accessions, not previously classified, were assigned to a species based on diagnostic RAPDs. Definitive conclusions about the species assignment of three other accessions were not possible. The level of diversity between Capsicum annuumaccessions from the genebank and the breeding program were compared and no differences were observed either for RAPD variation or diversity. The utilization of genetic resources as a source of variance for useful traits in the breeding program may be the reason for the similarity of these two groups.

Genetic Variation among Tomato Accessions from Primary and Secondary Centers of Diversity

The Asian Vegetable Research and Development Center (AVRDC) maintains one of the largest collections of Lycopersicon germplasm. Approximately 60% of the collection is from Old World regions; however, it is unclear whether these accessions represent unique sources of genetic variation compared with accessions from New World regions. The objective of this study was to compare the magnitude and structure of genetic variation among tomato accessions collected from Old and New World regions. Forty‐one random amplified polymorpbic DNA (RAPD) primers generated 98 polymorphic RAPD markers and were used to estimate relationships among 96 accessions collected from a wide geographic range. Genetic distances, marker frequency, and marker diversity were used to compare subpopulations of these accessions. Differences in RAPD marker frequencies indicated uniqueness of accessions from the New and Old World collections. In addition, accessions from Ecuador, Peru, and Chile had a larger magnitude of marker diversity than do Old World accessions. Comparison of sub‐populations of L. esculentum and its sub‐species, L. esculentum var. cerasiforme, indicated that the two are distinct but have similar levels of diversity. Variation among L. esculentum accessions can be obtained at a faster rate by sampling accessions from the primary center vs. other geographic regions. Yet Old World accessions complement accessions from the New World and are not simply redundant sources of variation.

Effects of intercropping and soil amendment with urea and calcium oxide on the incidence of bacterial wilt of tomato and survival of soil‐borne Pseudomonas solanacearum in Taiwan

Intercropping and soil amendment experiments were conducted to determine if they reduced populations of Pseudomonas solanacearum and bacterial wilt of tomato at the Asian Vegetable Research and Development Center (AVRDC) and at three other locations in Taiwan. At AVRDC, intercropping tomato with cowpea planted within the row significantly reduced bacterial wilt (P < 0.05) compared to when tomato was cropped alone. The P. solanacearum population in soil was not affected by intercropping with cowpea, soybean, or Welsh onion.At the same site, however, a preplanting soil amendment consisting of urea (200 kg ha−1 N) and CaO (5000 kg ha−1) significantly reduced the pathogen population and tomato bacterial wilt (P < 0.001). The effect of the soil amendment was not consistent when applied to soil from three other sites in Taiwan; in soil from two sites no reduction of the pathogen population occurred. At these sites, tomato bacterial wilt in the field was not reduced significantly after amending. In comparison with a non‐amended control, the addition of only CaO reduced the P. solanacearum population in AVRDC soil significantly (P < 0.05), but the reduction was significantly greater when the complete soil amendment was added. In contrast, urea alone did not affect the survival of P. solanacearum in the soil. In a greenhouse experiment with AVRDC soil, P. solanacearum was undetectable 2 weeks after soil amendment, but in the same treatment tomato yield was significantly reduced by 48% (P < 0.05) compared with non‐amended treatments. The suppressive effect of the soil amendment on the P. solanacearum population was probably due to the generation of one or several toxic substances during the transformation of urea in the presence of CaO.

RAPD Marker Facilitated Analysis of Genetic Diversity among Capsicum Genetic Resources from the Asian Vegetable Research and Development Center

Significant effort has been made in the collection of Capsicum germplasm throughout the world for maintenance by genebanks. The largest Capsicum germplasm collection is held by the Asian Vegetable Research and Development Center (AVRDC), consisting of 6844 accessions and eight species. The paradox of any germplasm collection is that, as the number of accessions and the probability of preserving genetic variability increases, the ability of users to efficiently utilize this resource decreases. Genetic variation can be quantified using RAPD molecular marker allele frequency and allelic variation to understand the genetic structure and variation within and among populations. The comprehensive Capsicum collection held at the AVRDC provides an opportunity to sample a range of germplasm representative of the variability that exists in available Capsicum germplasm. Accessions were sampled from the AVRDC collection to represent the range of genetic variation available in Capsicum 1) based on cluster analysis using morphological traits among 1500 accessions and 2) based on pedigree information from the Capsicum breeding program. Our objectives include understanding the structure and magnitude of genetic diversity among these AVRDC accessions and comparing the genetic diversity within sub-populations of these accessions. RAPD fingerprints of these accessions were collected using markers dispersed over numerous linkage groups based on a genetic map we have constructed. RAPD band frequencies and RAPD band diversity were used to test differences among and within sub-populations. The understanding of the distribution of genetic variation among and within these sub-populations will be useful for prioritizing collection, conservation, and sampling of these genetic resources.

Edamame Genotype Performance in Southwest Washington

Commercial edamame (Glycine max) varieties and advanced edamame breeding lines from the Asian Vegetable Research Development Center (AVRDC) were tested for adaptability to southwest Washington. Edamame, or green vegetable soybeans, are specialty varieties of soybeans that are eaten at the green stage as a vegetable. For the vegetable market, 25 beans must weigh at least 20 g. Experimental procedure was a randomized complete block design with four replications. Recommendations from AVRDC for plant spacing and fertilizer application and timing were followed. In 1995, 13 commercial varieties and 10 AVRDC breeding lines were tested in an on-farm location in Chehalis. At the same location in 1996, 10 of these commercial varieties were again tested along with an additional six commercial varieties. Also in 1996, 12 new AVRDC breeding lines were tested along with the single line that was selected in 1995. Both years, all commercial varieties were harvested more than 40 days later than their advertised days to maturity. Three commercial varieties, White Lion, Shironomai, and Butterbeans, were high-yielding in both years. In 1995, one AVRDC breeding line was selected in Chehalis, and in 1996 five additional AVRDC breeding lines were selected. Earliness is a key factor affecting suitability of commercial varieties and breeding lines to the Chehalis area. In this region, irrigation also appears essential for production of large beans for the vegtable market. Pod weight was not a good indicator of bean weight. Seed was collected in Chehalis from AVRDC breeding lines for use in future trials.

AC Harosprout mungbean

AC Harosprout is a medium to full-season-maturing and high-yielding mungbean [Vigna radiata (L.) Wilczek] cultivar. It is adapted to southwestern Ontario for the production of green beans for sprouting and other human uses. It was purified from an introduction VC1973A from the Asian Vegetable Research and Development Centre (AVRDC). Key words: Vigna radiata, mungbean, green bean, green gram, bean sprout, cultivar description

DEVELOPMENT OF A NEURAL NETWORK FOR SOYBEAN RUST EPIDEMICS

The objective of this study was to develop a neural network to predict soybean rust disease severity for a single soybean cultivar. Data available for development consisted of sequential weekly plantings of TK 5 soybean cultivar in 1980 and 1981, planted at the Asian Vegetable Research and Development Center in Taiwan. Plant and disease development were measured weekly throughout the season for each planting date experiment. Data from 73 epidemics were collected with a total of 577 scenarios (observations) over the two years. A total of seven inputs related to soybean and rust progress and weather were available for development. Validation was performed for two different assumptions about the independence of the epidemics. In the first validation, it was assumed that all epidemics were independent. The 73 epidemics and their associated observations of rust severity were selected so that 70% were used for training, 15% for testing, and 15% for validation. Several different three-layer feedforward neural networks were developed using different combinations of inputs and hidden nodes. The best NN had four inputs and four hidden nodes, and gave the highest coefficient of multiple determination (R2) of 0.793 for the validation scenarios. This configuration gave the lowest average error of 11.0% per observation. Cumulative probability of percent error between predicted and observed rust severity showed that 50% of the validation scenarios had errors within ±10% of measured values, and 80% had errors within ±20%. In the second validation, it was assumed that epidemics in 1980 were independent of epidemics in 1981. Epidemics for 1980 were used for training and testing, and epidemics in 1981 were used for validation. Several different three-layer feed forward networks were developed with different combinations of inputs and hidden nodes. Networks with three and four inputs gave very similar results. The three input network gave an R2 of 0.858, average error of 9.7%, and a maximum error of 43% for the validation scenarios. Cumulative probability of percent error between predicted and measured rust severity showed that 54% of the validation scenarios had errors within ±10%, and 84% of the scenarios had errors within ±20% of measured values.

Differential interactions ofPhytophthora capsici isolates with pepper genotypes at various plant growth stages

Pepper cultivars from diverse geographic origins were evaluated for resistance to different isolates ofPhytophthora capsici under controlled environmental conditions. All accessions tested were susceptible at the four-leaf stage to the six isolates ofP. capsici. Inoculation at the eight-leaf stage resulted in significantly different interactions among the accessions andP. capsici isolates. The Korean and U.S. cultivars tested were highly susceptible to the isolates ofP. capsici at this stage. In contrast, PI 201234 and PI 201238 had a differential interaction with someP. capsici isolates. At the twelve-leaf stage, Phytophthora blight developed slowly in the Korean and U.S. cultivars that were highly susceptible at the eight-leaf stage. Furthermore, the accessions from the Asian Vegetable Research and Development Center (AVRDC) became highly resistant toP. capsici at this stage.

Variable Reaction of Tomato Lines to Bacterial Wilt Evaluated at Several Locations in Southeast Asia

Bacterial wilt (BW), caused by Pseudomonas solanacearum E.F. Smith, is one of the most destructive disease of tomato (Lycopersicon esculentum Mill.) in the tropics. Twenty tomato lines/accessions previously identified as BW-resistant were evaluated for BW reaction in fields providing high disease pressure at Subang, Indonesia; Los Baños, Philippines; Malaysian Agricultural Research and Development Institute (MARDI), Kuala Lumpur; Asian Vegetable Research and Development Center (AVRDC), Taiwan; and Taiwan Seed Improvement and Propagation Service (TSIPS). Entries also were tested in the greenhouse at the AVRDC with a P. solanacearum strain from Taiwan (Pss4) using a drench inoculation method. Objectives of the study were to identify stable sources of BW resistance for southeast Asian tomato breeding programs, and to determine the correlation between field and greenhouse reactions. Mean entry survival was 21.6% at Subang, 31.9% at Los Baños, 76.7% at the AVRDC, 93.6% at Malaysia, and 93.3% at TSIPS, indicating that most entries were resistant at MARDI and the Taiwan locations but susceptible at Subang and Los Baños. L285 (mean survival = 83.8%) and CRA 84-58-1 (mean survival = 79.4%) were the most resistant entries in the field trials. Mean survival (70.1%) of CRA 66-derived entries was significantly better than the mean of entries with resistance derived from UPCA 1169 or UPCA 1169 plus `Venus' or `Saturn'. Mean survival of AVRDC entries bred in the 1980s (59.4%) was significantly greater than mean survival of AVRDC lines bred in the 1970s (45.7%). The correlation between entry BW percent survival averaged over the five field trials and entry means from drench inoculation in the greenhouse was highly significant (r = 0.70), suggesting that the drench inoculation method is effective in selection for BW resistance.

Late blight ( Phytophthora infestans) on tomato in the tropics

Of all the pathogens of economically important plant species, Phytophthora infestans (Mont.) de Bary can rightly claim its place as the most notorious. Its occurrence in Ireland during the last century caused both the potato famine of 1846-49 and the establishment ofplant pathology as a scientific discipline by Rev. M. J. Berkeley and others. Even today, late blight frequently decimates potato crops during wet summers, despite significant advances in disease prediction, crop protection (usually with phenyl amide or dithiocarbamate fungicides) and the introduction of more resistant cultivars. Although' late blight has traditionally been associated with potatoes, in tropical climates with periods of high rainfall the same pathogen can be a significant factor limiting yields from tomato crops. In many developing countries, tomato represents an important food crop, not only because of the high price it commands compared to staples such as rice, but also because it provides a valuable source of vitamins when fresh and improves the flavour of meals when cooked. The requirement of tomatoes for moderately low night-time temperatures for efficient fruit-set limits production in the lowland tropics to the cooler seasons. Consequently summer production is centred upon cooler upland areas (e.g. in the Cameron Highlands of Malaysia and the Central African massif), where high rainfall levels are optimal for late blight infection. In such areas, late blight represents a serious problem, since application of costly imported fungicide is often ineffective due to dilution by rainfall and the potential occurrence offungicide-resistant strains of the pathogen. Research at the University of Wales, Bangor being funded by the UK Government Overseas Development Administration and in collaboration with the Asian Vegetable Research and Development Centre (AVRDC) in Taiwan has two objectives. Firstly, we are identifying promising sources of resistance to late blight by screening material from tomato germplasm collections; promising accessions are currently being field-tested in Taiwan, Tanzania and Costa Rica prior to the initiation of a breeding programme. Secondly, we are examining levels of genetic variability within populations of the pathogen from tropical areas; it is vital to know the extent of geographical variation in the aggressiveness and virulence within pathogen populations to maximize the possibility that resistance factors introduced into planting material will provide durable disease protection over a wide geographical range. An important component of our research therefore involves the acquisition of samples of the pathogen from a range of countries, both temperate and tropical. These will permit testing the resistance of promising tomato accessions against pathogens from the countries where the resistant cultivars will ultimately be grown. A further reason for wishing to assess P. infestans populations is the increase over recent decades in the international potato trade. The concomitant migration of the fungus in diseased tubers is believed to have led to significant population changes. We hope that by obtaining isolates ofthe fungus from around the world it will be possible to more accurately monitor these changes. Wherever tomatoes are grown without irrigation and without heavy use of fungicides, it is likely that late blight is present unless conditions are very dry. The symptoms include blackening of the leaves (Fig Ia; often spreading lesions originating from the tip of the leaf) and death of whole branches of the plant (Fig Ib). Infected green fruit become marbled brown in appearance (Fig Ic) without becoming soft (not to be confused with nutritional disorders such as blossom end rot, which usually affect the area around the tip of the fruit). Sporulation of the fungus (only under

Inheritance of black leaf mold resistance in tomato

Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC1F2-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC1F2-358-4-13 and CL5915-93D4-1-0-3). For each cross, six generations, i.e. P1, P2, F1, F2, BC1F1 and BC1F2 were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F2 in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC1F2 data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.