Ukrainian breeders from Institute of Potato Research and nematologists from Institute of Plant Protection have been breeding potato cultivars for resistance to potato cyst nematode Globodera rostochiensis, pathotype Ro1 since 1994. Three new nematode resistant potato cultivars (Dnipryanka, Zahadka, Lileya) have been bred since then. These cultivars belong to different maturity groups and have many characters of economic importance (high yield potential, good taste quality, disease resistance).

Modern phytopathological situation that has formed on the potato crop in Belarus is presented and the main problems are determined. It was considered that efficiency of potato breeding for disease resistance depends on solution of them

Viral diseases of sweet potato are very prevalent and often seriously damaging to the plants. In particular, the severe strain of the sweet potato feathery mottle virus (SPFMV-S) causes 'obizyo-sohi' disease in Japan. In order to confer viral resistance against SPFMV using current biotechnology, a transgenic sweet potato has been produced, introducing hygromycin-resistant (hpt) and SPFMV-S coat protein (CP) genes, which have shown a significant resistance to SPFMV-S. In the breeding programme, it is important to confirm that the viral resistance conferred in T0 plants can be inherited by their progeny. In the present study, progeny were obtained from crosses between the transgenic T0 and a non-transgenic variety of sweet potato. The results showed that the CP gene was inherited by the next generation and that the stability of viral resistance was also confirmed. Thus, this production system for the virus-resistant transgenic sweet potato is useful in practical breeding.

Late blight caused by the oomycete Phytophthora infestans is the most destructive disease in potato cultivation worldwide. New, more virulent P. infestans strains have evolved which overcome the genetic resistance that has been introgressed by conventional breeding from wild potato species into commercial varieties. R genes (for single-gene resistance) and genes for quantitative resistance to late blight are present in the germplasm of wild and cultivated potato. The molecular basis of single-gene and quantitative resistance to late blight is unknown. We have cloned R1, the first gene for resistance to late blight, by combining positional cloning with a candidate gene approach. The R1 gene is member of a gene family. It encodes a protein of 1293 amino acids with a molecular mass of 149.4 kDa. The R1 gene belongs to the class of plant genes for pathogen resistance that have a leucine zipper motif, a putative nucleotide binding domain and a leucine-rich repeat domain. The most closely related plant resistance gene (36% identity) is the Prf gene for resistance to Pseudomonas syringae of tomato. R1 is located within a hot spot for pathogen resistance on potato chromosome V. In comparison to the susceptibility allele, the resistance allele at the R1 locus represents a large insertion of a functional R gene.

Bacterial soft rot caused by Erwinia carotovora subsp. carotovora is a major disease in Zantedeschia spp., particularly in cultivars from the section Aestivae. The disease can be partly controlled by cultural measures, but by combining cultural methods with resistant plant material a promising strategy for control of soft rot can be developed. No tests are available for resistance testing in breeding Zantedeschia spp. Therefore, three tests developed for use in potato breeding were adapted for use on eight cultivars of Zantedeschia spp. Variation was found in all three tests. Resistant control cultivar Zantedeschia aethiopica 'Crowborough' scored most resistant in all three tests. Within the section Aestivae, degrees of susceptibility were identified that were in agreement with each other and with field observations, indicating reliability of two of the methods in which tubers were used. The correlation coefficient of these two tests was high. A new non-destructive test method was developed for use on seedlings which involved immersion of leaf disks in a bacterial suspension. The percentage of decayed leaf area was a measure of resistance and results were in general agreement with the other tests. These methods will be useful for breeding for soft rot resistance and performing genetic analyses.

One of the most serious diseases of the potato crop worldwide is late blight caused by Phytophthora infestans (Mont.) de Bary. Most growers control the disease by applying fungicides at regular intervals of 8-10 days from the time of row closing until the end of the growing season. The NEGFRY model is used for timing the chemical control of potato late blight. The NEGFRY model is based on two existing models, the "negative prognosis", for forecasting the risk of primary attacks, and a model for timing subsequent fungicide applications during the season. The main objective of NEGFRY is to get high yield and quality with minimum use of fungicides. Present work underlies the experiments that were arranged in 2000 and 2001 at the Jogeva Plant Breeding Institute. Two potato varieties with different resistance to late blight were taken to the experiment in both years: susceptible 'Adora' and modarately resistant 'Anti' in the year 2000 and susceptible 'Berber' and 'Anti' in 2001. NEGFRY gave highest economical effect among six tested treatment regimes.

Early blight, caused by Alternaria solani Sorauer, is a serious disease of potatoes that occurs in most potato growing regions in the world. There is little resistance to early blight among commercial potato cultivars. However, resistance to early blight in diploid (Solanum phureja- S. stenotomum) potatoes has been identified, and was found to be highly heritable and readily transferred to the tetraploid level via 4x-2x crosses. The purposes of this study were to identify good levels of early blight resistance in open-pollinated 4x-2x (Solanum tuberosum x S. phureja- S. stenotomum) hybrids selected for horticultural characteristics, to estimate broad-sense heritability for early blight resistance in these hybrids, and to investigate the general and specific combining ability for resistance to early blight from some of these early blight resistant tetraploid selections. Four early blight resistant clones were crossed as female parents with four different male parents in a design II mating scheme to generate 16 families. Approximately 20 randomly chosen offspring per family were visually evaluated for early blight resistance in 1995 and 1996 in a randomized complete block design in Pennsylvania. Broad-sense heritability for early blight resistance among the open-pollinated 4x-2x hybrids which were originally selected for horticultural characteristics was 0.91 with a 95% confidence interval of 0.80, 0.94. There were significant differences among female and male parents for area under the disease progress curve, indicating the importance of general combining ability for early blight resistance in this germplasm. The female x male source of variation was not significant, indicating that specific combining ability was not important. The greatest number of resistant progeny were observed in families where both parents were derived from the early blight resistant population; however, at least one highly resistant progeny was produced in all families. These results suggest that the early blight resistance in these clones can be readily incorporated into the commercial tetraploid breeding population.

Sweetpotato virus disease (SPVD) is a disease syndrome due to the dual infection and synergistic interaction of sweetpotato chlorotic stunt crinivirus (SPCSV) and sweetpotato feathery mottle potyvirus (SPFMV). SPVD causes up to 98% yield loss in East Africa. Uganda’s sweetpotato breeding program released six sweetpotato cultivars with moderate to high levels of field SPVD resistance in 1995. A multidisciplinary partnership involving Namulonge Agricultural and Animal Production Research Institute in Uganda, North Carolina State University, the US Vegetable laboratory (USV, USDA-ARS) and Clemson University, Charleston, South Carolina, and the International Potato Center (CIP), Lima, Peru, has investigated the genetic basis of SPVD resistance. This paper highlights research findings of the response of sweetpotato to sweetpotato virus disease. General combining ability (GCA) and specific combining ability of (SCA) of 45 sweetpotato diallel families, and the GCA to SCA variance component ratios were high, indicating that additive gene effects are predominant in the inheritance of SPVD and recovery. The distribution of SPVD scores in the promising families was skewed toward highly susceptible categories in Uganda and Peru. In the proposed model for inheritance, two genes are unlinked and they are inherited in a hexosamic or tetradisomic manner. Based on amplified fragment length polymorphism (AFLP) and quantitative trait loci (QTL) analyses, two unlinked AFLP markers were associated with the loci conferring resistance to SPCSV and SPFMV.

An in vitro method for assessing cassava anthracnose disease (CAD) resistance was developed as a preliminary screen to a CAD‐resistant breeding programme. Potato dextrose agar (PDA) media was amended by extracts from the stem cortex of 10 cassava cultivars (30001; 30572, 30211, 88/02549, 88/00695, 88/01336, 91/00344, 91/00313, 91/00684 and 91/00475), and assayed for efficacy of inhibition of the growth of Colletotrichum gloeosporioides f. sp. manihotis isolates (05FCN, 10FCN, 12FCN, and 18FCN). Morphological and physiological data indicated that there was a significant difference (P ≤ 0.05), in mycelial growth, spore germination and sporulation among the four isolates on PDA amended with cassava stem extracts. Extracts from cassava cultivars 30211, 91/00684 and 91/00313 showed higher inhibition of germ tube development, mycelial growth and sporulation of the fungal isolates, whereas cultivars 88/02549 and 88/01336 showed the least inhibition. The 10 cultivars were further tested in both greenhouse and field conditions, under disease pressure for two planting seasons, to corroborate resistance to the fungus as observed in vitro. Greenhouse and field trials with the 10 cassava cultivars showed a significant difference (P ≤ 0.05) in CAD resistance. Cultivars 88/02549 and 88/01336 were highly CAD‐susceptible, as shown in the in vitro assays and confirmed in the greenhouse and field tests. The other eight cultivars were either resistant (30211, 91/00684), or moderately resistant (30572, 88/00695, 91/00475, 91/00344, 30001 and 91/00313) to CAD. The study shows that an in vitro screening assay of cassava for resistance to CAD could serve as a convenient preliminary screening technique to discriminate CAD‐resistant from CAD‐susceptible cassava cultivars. The in vitro screening method considerably reduces time and labour in comparison with the current screening techniques of cassava, which involve field planting, inoculation and evaluation.

No Brasil a ocorrência de mosaico causado por PVY é relatada desde 1941 na cultura da batata, mas sua ocorrência em pimentão só foi relatada a partir de 1950. As perdas causadas por essa virose no campo levaram ao estabelecimento de um programa de melhoramento do pimentão visando a incorporação de genes de resistência a PVY, dando origem à série de cultivares "Agronômico". A resistência a PVY introduzida na série Agronômico mostrou- se bastante eficiente e duradoura, conseguindo impedir a infecção por todas as estirpes de PVY então presentes no Brasil. No entanto, relatos de mosaico, deformações foliares e acentuada redução no crescimento das plantas vem sendo realizados por produtores de diversos estados nos últimos cinco anos. O objetivo principal deste trabalho foi estudar a etiologia do mosaico em campos de produção de pimentão e pimenta. Vinte e um isolados virais provenientes de plantas de pimenta e pimentão foram coletados em campos de produção em Minas Gerais, São Paulo, Espírito Santo, Rio de Janeiro e Distrito Federal. Dois isolados provenientes de batata (PVYn e PVYø ) foram utilizados como controle. Para caracterizar e diferenciar biologicamente estes vinte isolados utilizou-se um gama de hospedeiros e uma série de cultivares diferenciadoras de pimentão. As indicadoras utilizadas mostraram a existência de um considerável grau variabilidade biológica entre os isolados em estudo, embora todos tenham sido identificados como PVY. As reações diferenciais de algumas espécies distinguiram os isolados de outros potyvírus que infectam pimentão. Foi possível observar, de maneira generalizada, a distinção de três grupos de isolados, causando sintomas severos, moderados ou fracos, em várias das hospedeiras utilizadas. A reação das cultivares diferenciadoras classificou os isolados como patótipo 1 ou 1.2 do PVY. Não foi encontrado nenhum representante do patótipo 0. A produção de anti-soro foi realizada utilizando-se como imunógeno partículas virais purificadas de um isolado severo e um isolado fraco. O título e a especificidade dos anti-soros foram avaliados por ELISA indireto. Reações positivas foram obtidas com uma diluição do anti-soro bruto acima de 1:32.000. Reações positivas também foram observadas contra isolados distintos, mas não contra todos os isolados testados. Os anti-soros não reagiram contra o isolado PVY O de batata, mas reagiram contra o isolado PVYn, também de batata. Para caracterização molecular dos isolados foi realizada a clonagem e sequenciamento dos genes nib, cp e da região 3' não-traduzida (3 ́NTR) de isolados biologicamente distintos. Após análise filogenética confirmou-se a identidade de seis isolados como pertencentes à espécie Pepper yellow mosaic virus (PepYMV), um potyvírus descrito em 2002 infectando pimentão no Brasil. Esse resultado sugere que o PepYMV pode ser a espécie de potyvírus predominante em Capsicum no Brasil. | In Brazil, the mosaic caused by PVY was reported for the first time in 1941 in potato. The first report of this virus infecting bell pepper occurred only in 1950. The heavy losses caused by the disease in pepper plants led to the establishment of a breeding program with the objective of obtaining PVY- resistant cultivars. This program generated the "Agronômico" series of pepper cultivars in the early 1970's. The resistance present in the "Agronômico" series was durable and extremely effective against all the viral strain present in Brazil at the time. However, reports of mosaic, lead distortion and growth reduction symptoms in pepper plants have occurred repeatedly over the last five years. The main objective of this work was the study the etiology of the disease in bell pepper and chili pepper fields. Twenty-one isolates were obtained from bell pepper and chili pepper plants in the states of Minas Gerais, São Paulo, Espírito Santo, Rio de Janeiro and the Federal District. Two isolates from potato (PVY N e PVY O ) were used as controls. The isolates were biologically characterized using a host range assay and inoculation into a series of differential bell pepper cultivars. The isolates displayed a high degree of biological variability upon inoculation onto the indicator plants used in the host range assay, although they could all be identified as PVY. Some host species could be used to distinguish the isolates from other viruses that also infect bell pepper. In general, it was possible to divide the isolates in three groups, causing severe, moderate and mild symptoms in several host species. The reaction of the differential cultivars allowed the classification of the isolates as pathotypes 1 or 1.2 of PVY. None of the isolates were classified as pathotype 0. The production of anti-sera was carried out using purified virions of a mild and a severe isolate. The titer and specificity of the anti-sera were evaluated by indirect ELISA. Positive reactions were obtained with a dilution of the crude serum up to 1:32.000. Positive reactions were also observed against most, but not all the isolates. The anti-sera did not react against the PVYø isolate from potato, but did react against the PVY N isolate, also from potato. For the molecular characterization, the nib and cp genes and the 3' non-translated region (3 ́NTR) of biologically distinct isolates were cloned and sequenced. Sequence and phylogenetic analysis confirmed the identity of six isolates as Pepper yellow mosaic virus (PepYMV), a potyvirus first described in 2002 infecting bell pepper in Brazil. This result suggests that PepYMV could be the predominant potyvirus causing mosaic in Capsicum species in Brazil. | Coordenação de Aperfeiçoamento de Pessoal de Nível Superior