Development Of Resistant Cultivars Research Articles

Transmitting Plant Viruses Using Whiteflies

Whiteflies, Hemiptera: Aleyrodidae, Bemisia tabaci, a complex of morphologically indistinquishable species5, are vectors of many plant viruses. Several genera of these whitefly-transmitted plant viruses (Begomovirus, Carlavirus, Crinivirus, Ipomovirus, Torradovirus) include several hundred species of emerging and economically significant pathogens of important food and fiber crops (reviewed by9,10,16). These viruses do not replicate in their vector but nevertheless are moved readily from plant to plant by the adult whitefly by various means (reviewed by2,6,7,9,10,11,17). For most of these viruses whitefly feeding is required for acquisition and inoculation, while for others only probing is required. Many of these viruses are unable or cannot be easily transmitted by other means. Therefore maintenance of virus cultures, biological and molecular characterization (identification of host range and symptoms)3,13, ecology2,12, require that the viruses be transmitted to experimental hosts using the whitefly vector. In addition the development of new approaches to management, such as evaluation of new chemicals14 or compounds15, new cultural approaches1,4,19, or the selection and development of resistant cultivars7,8,18, requires the use of whiteflies for virus transmission. The use of whitefly transmission of plant viruses for the selection and development of resistant cultivars in breeding programs is particularly challenging7. Effective selection and screening for resistance employs large numbers of plants and there is a need for 100% of the plants to be inoculated in order to find the few genotypes which possess resistance genes. These studies use very large numbers of viruliferous whiteflies, often several times per year. Whitefly maintenance described here can generate hundreds or thousands of adult whiteflies on plants each week, year round, without the contamination of other plant viruses. Plants free of both whiteflies and virus must be produced to introduce into the whitefly colony each week. Whitefly cultures must be kept free of whitefly pathogens, parasites, and parasitoids that can reduce whitefly populations and/or reduce the transmission efficiency of the virus. Colonies produced in the manner described can be quickly scaled to increase or decrease population numbers as needed, and can be adjusted to accommodate the feeding preferences of the whitefly based on the plant host of the virus. There are two basic types of whitefly colonies that can be maintained: a nonviruliferous and a viruliferous whitefly colony. The nonviruliferous colony is composed of whiteflies reared on virus-free plants and allows the weekly availability of whiteflies which can be used to transmit viruses from different cultures. The viruliferous whitefly colony, composed of whiteflies reared on virus-infected plants, allows weekly availability of whiteflies which have acquired the virus thus omitting one step in the virus transmission process.

Study relationship of drought tolerance indices in wheat (Triticum aestivum) genotypes

Drought is a wide-spread problem seriously influencing wheat (Triticum aestivum) production and quality, but development of resistant cultivars is hampered by the lack of effective selection criteria. The objective of this study was to evaluate the ability of several selection indices to identify drought resistance cultivars under drought stress conditions. Eight wheat cultivars (Triticum aestivum) were chosen for the study based on randomized complete block design with three replications in the greenhouse. The resulting of this study showed that the breeders should choose the indices on the basis of stress severity in the target environment; GMP, HARM, MP and STI were suggested as useful indicators for wheat breeding and on basis of this index genotypes 2022, Alvand and 2021 introduced as tolerant genotypes. The best indices for selecting tolerant species were GMP, HARM, MP and STI. Therefore genotypes which had higher amount of these indices identified as the most tolerant genotypes.

Biological and genetic diversity of plasmodiophorid-transmitted viruses and their vectors

About 20 species of viruses belonging to five genera, Benyvirus, Furovirus, Pecluvirus, Pomovirus and Bymovirus, are known to be transmitted by plasmodiophorids. These viruses have all positive-sense, single-stranded RNA genomes that consist of two to five RNA components. Three species of plasmodiophorids are recognized as vectors: Polymyxa graminis, P. betae, and Spongospora subterranea. The viruses can survive in soil within the long-lived resting spores of the vector. There are biological and genetic variations in both virus and vector species. Many of the viruses are causal agents of important diseases in major crops such as rice, wheat, barley, rye, sugar beet, potato, and groundnut. Control is dependent on the development of resistant cultivars. During the last half century, several virus diseases have rapidly spread worldwide. For six major virus diseases, we address their geographical distribution, diversity, and genetic resistance.

Evaluation of Resistance to TYLCV (Tomato Yellow Leaf Curl Virus) in Tomato (Lycopersicum esculentum Mill.) Breeding Lines

Tomato TYLCV is difficult to prevent by chemicals or other methods Thus, developmentof resistant cultivar is certainly needed. Especially, a resistant cultivar is required that show increased resistance through the accumulation of individual TYLCV resistance gene, Ty-1,2 and 3 (partial dominance). The phenotype of resistance was surveyed by the infection of whiteflies against 7 lines such as TYLCV resistant line (11-TY1-AV), susceptibility-control cultivar (11-TY5-AV), 3 lines of F3-generation and 4 lines of F2-generation. These cultivar and lines were artificially inoculated by TYLCTHV strain. The susceptible symptom could be confirmed at one week after the inoculation. After 10 days of inoculation, 83% of susceptible control showed the infected symptom. After 13 days, 100% of the control showed the TYLCV symptom. However, 16 individuals was infected out of 44 individuals in 11-TY4-AV and 12 individuals was infected out of 38 individuals in 11-TY6-AV. Eight individuals was infected out of 43 individuals in 1-TY7-AV, and 11 individuals was infected out of 42 individuals in 11-TY8-AV. Regarding these results, the genetic segregation ratio (3 : 1) in phenotype of 4 lines of F2 generation is following the Mendelism in all lines. Also, it could be confirmed that the resistance level is depending on maternal lines even with same paternal line that is resistant to TYLCV.

Development of Genetic Markers Linked to Straighthead Resistance through Fine Mapping in Rice (Oryza sativa L.)

Straighthead, a physiological disorder characterized by sterile florets and distorted spikelets, causes significant yield losses in rice, and occurs in many countries. The current control method of draining paddies early in the season stresses plants, is costly, and wastes water. Development of resistant cultivar is regarded as the most efficient way for its control. We mapped a QTL for straighthead resistance using two recombinant inbred line (RIL) F9 populations that were phenotyped over two years using monosodium methanearsonate (MSMA) to induce the symptoms. One population of 170 RILs was genotyped with 136 SSRs and the other population of 91 RILs was genotyped with 159 SSRs. A major QTL qSH-8 was identified in an overlapping region in both populations, and explained 46% of total variation in one and 67% in another population for straighthead resistance. qSH-8 was fine mapped from 1.0 Mbp to 340 kb using 7 SSR markers and further mapped to 290 kb in a population between RM22573 and InDel 27 using 4 InDel markers. SSR AP3858-1 and InDel 11 were within the fine mapped region, and co-segregated with straighthead resistance in both RIL populations, as well as in a collection of diverse global accessions. These results demonstrate that AP3858-1 and InDel 11 can be used for marker-assisted selection (MAS) for straighthead resistant cultivars, which is especially important because there is no effective way to directly evaluate straighthead resistance.

Management of Bacterial Wilt [Rhalstonia solanacearum Yabuuchi et al., 1995] of Potatoes: Opportunity for Host Resistance in Kenya

This article gives a general overview of bacterial wilt of potatoes and its management. It also highlights the potential of host resistance as an important component of integrated management of bacterial wilt in Kenya. Bacterial wilt has spread to all potato growing areas in Kenya, affecting over 70% of potato farms and causing yield losses of between 50 to 100%. This disease has no effective means of control because crop protection chemicals are ineffective and expensive and biological control agents are ineffective. In addition, phytosanitary methods such as quarantine are either expensive or difficult to apply and cultural methods such as crop rotations are largely impractical because the farms are too small to allow effective rotation, the pathogen has a wide host range, and it persists for long in the soil. Development of resistant cultivars could therefore play an important role in managing the disease. More resistant potato clones have recently been identified by CIP scientists, and this resistance needs to be incorporated into the popular but susceptible Kenyan potato cultivars so as to increase potato production in Kenya. For better results, use of high resistant varieties may be coupled with use of disease-free tubers and clean fields.

Population Structure, Linkage Disequilibrium, and Genetic Diversity in Soft Winter Wheat Enriched for Fusarium Head Blight Resistance

The occurrence of epidemics of Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, in U.S. winter wheat (Triticum aestivum L.) during the past two decades led to signifi cant emphasis on development of resistant cultivars. Understanding the genetic diversity, population structure (PS), and linkage disequilibrium (LD) in winter wheat in the eastern United States is important for marker-assisted breeding and association analysis in this germplasm. Lines selected from collaborative FHB screening nurseries were genotyped with simple sequence repeat (SSR), sequence tagged site (STS), and Diversity Array Technology (DArT) markers to assess LD, genetic diversity, and PS. The genomewide average of LD decay to r 2 0.2) were generally constrained to markers less than 5 cM apart. Although the lines evaluated were targeted to distinct production zones of the eastern winter wheat region, cluster and principal component analyses did not detect separation of lines into subpopulations. The short, intense breeding history for scab resistance may have localized effects on LD. Lack of subgroups within our population could be due to intercrossing among common resistant parents and indicate frequent admixture and germplasm exchange among U.S. winter wheat programs focused on development of FHB resistant cultivars. F USARIUM HEAD BLIGHT (FHB), caused by Fusarium graminearum Schwabe, is a disease of wheat of international importance. Although the most economical

Screening ofBrassicagermplasm for resistance toPlasmodiophora brassicaepathotypes prevalent in Canada for broadening diversity in clubroot resistance

Hasan, M. J., Strelkov, S. E., Howard, R. J. and Rahman, H. 2012. Screening of Brassica germplasm for resistance to Plasmodiophora brassicae pathotypes prevalent in Canada for broadening diversity in clubroot resistance. Can. J. Plant Sci. 92: 501–515. Clubroot disease of crucifers, caused by Plasmodiophora brassicae, poses a threat to the Canadian canola industry, and the development of resistant cultivars is urgently needed. Germplasm resistant to local pathotype(s) is the prime requirement for breeding clubroot-resistant cultivars. The objective of this study was to identify Brassica germplasm possessing resistance to P. brassicae pathotypes prevalent in Alberta. Pathotype-specific resistance was identified in the diploid species Brassica rapa (AA) and B. oleracea (CC), and in the amphidiploid B. napus (AACC). Among B. rapa genotypes, turnip was the most resistant, followed by winter type and spring type oilseed rape. The rutabaga group of B. napus, on the other hand, was homogeneous for resistance to Canadian P. brassicae pathotypes. The diploid species B. nigra (BB) also showed pathotype-specific resistance. However, the two amphidiploids carrying the B. nigra genome, B. juncea (AABB) and B. carinata (BBCC) were completely susceptible to clubroot.

Screening of Brassica germplasm for resistance to Plasmodiophora brassicae pathotypes prevalent in Canada for broadening diversity in clubroot resistance

Hasan, M. J., Strelkov, S. E., Howard, R. J. and Rahman, H. 2012. Screening ofBrassicagermplasm for resistance toPlasmodiophora brassicae pathotypes prevalent in Canada for broadening diversity in clubroot resistance. Can. J. Plant Sci. 92: 501–515. Clubroot disease of crucifers, caused by Plasmodiophora brassicae, poses a threat to the Canadian canola industry, and the development of resistant cultivars is urgently needed. Germplasm resistant to local pathotype(s) is the prime requirement for breeding clubroot-resistant cultivars. The objective of this study was to identify Brassica germplasm possessing resistance to P. brassicae pathotypes prevalent in Alberta. Pathotype-specific resistance was identified in the diploid species Brassica rapa (AA) and B. oleracea (CC), and in the amphidiploid B. napus (AACC). Among B. rapa genotypes, turnip was the most resistant, followed by winter type and spring type oilseed rape. The rutabaga group of B. napus, on the other hand, was homogeneous for resistance to Can...

Agro-morphological and phenological attributes under irrigated and rain-fed conditions in bread wheat genotypes

Drought is a wide-spread problem seriously influencing wheat production and quality, but development of resistant cultivars is hampered by lack of effective selection criteria. Based on recent rates of increase, the world population is expected to double from 6 billion in the next 50 years. Proper management of input using modern technology, particularly irrigation water management, is essential to maximize crop production and return for the farmers. Fourteen wheat genotypes (Triticum aestivum L.) were grown under two environments (irrigated and rain-fed) to determine morphological and phenological responses to drought. The results of combined analysis of variance for spike length, awn length, peduncle length, plant height, days to heading, grains/spike and grain yield indicated that genotypic differences were significant (P<0.01). No significant effect was observed for spike length under each of stress and non-stress conditions. The highest peduncle length was observed for Marvdasht followed by M-83-6 and M-81-13 under rain-fed conditions. Grain yield was positively correlated with spike length, peduncle length and grain/spike, but negatively correlated with plant height in the both environments. Average grain yield in rain-fed conditions was 11.26% lower than that in irrigated conditions. Marvdasht cultivar (G13) had the highest grain yield in both conditions, while the lowest grain yield belonged to accessions 1 and 4 (Hamam-4). Marvdasht, M-81-13, WS-82-9, PYN and Shiraz were the most productive genotypes in irrigated conditions but in rain-fed site, Marvdasht followed by M-81-13, M-83-6, STAR, M-79-7 and TEVEES had the highest grain yield. Marvdasht was the superior wheat genotype under both rain-fed and irrigated conditions. Key words: Awn length, drought, peduncle length, spike length, wheat genotypes.

Substitution mapping of QTLs for blast resistance with SSSLs in rice (Oryza sativa L.)

Rice blast, caused by fungal pathogen Magnaporthe grisea Barr., is one of the most devastating rice diseases worldwide. It has greatly affected the rice production and quality. Development of resistant cultivars is the most effective and economical way for controlling this disease in rice. In this study, 114 of the single-segment substitution lines (SSSLs) in rice were inoculated at seedling stage by 16 rice blast isolates. The substituted segments in the 114 SSSLs distributed on 12 chromosomes with coverage of 57.32% of rice genome. Fifteen of the SSSLs were different in blast resistance from the HJX74 recipient. The SSSL W23-7-6-5-2-2 showed 100% of resistance frequency. A total of 11 QTLs for blast resistance were detected on chromosomes 1, 2, 3, 6, 10, 11 and 12 in rice. They were mapped at chromosomal intervals of 2.2–46.2 cM, of which 6 QTLs were mapped at less than 10.0 cM. Six of the 11 QTLs were first reported in this paper.

Resistance of Tomato Subsamples to Bemisia tabaci Biotype B (Genn.) (Hemiptera: Aleyrodidae)

Whitefly (Bemisia tabaci) causes damage to tomato (Solanum lycopersicum L.) and is controlled by insecticides harmful to man and the environment. Development of resistant cultivars is ideal for whitefly management, with alternate genetic sources being indispensable. Germplasm banks are potentially good sources of resistant cultivars. Agronomic characteristics of the tomato subsamples from the Horticultural Germplasm Bank (HGB) at Universidade Federal de Viçosa (UFV) have been typified but little is known about their insect resistance. Thus, the objective of this study was to assess the resistance of 103 HGB‐UFV tomato subsamples to B. tabaci as well evaluate the resistance mechanism. The characteristics of the subsamples evaluated were the number of nymphs and eggs per plant and the resistance index compared with the susceptible cultivar Santa Clara, arbitrarily chosen as the susceptible standard. The trichome number per 0.04 cm2 of the leaf blades and 15 leaf hydrocarbon concentrations were also determined. Resistant subsamples were submitted to antibiosis test and the mortality (%) and life cycle of the B. tabaci were evaluated. The difference in the number of eggs per plant, nymphs per plant, and nymph/egg ratio in the tomato subsamples was evaluated. A positive correlation was observed between the hydrocarbons undecane and tridecane with B. tabaci nymphs. Significant and positive differences in the trichome per 0.04‐cm2 density were found between the trichome density and the number of eggs per plant. The subsamples HGB‐225, ‐327, ‐630, ‐813, ‐985, ‐2029, ‐2030, ‐2055, ‐2057, ‐2060, ‐2062, and ‐2068 were resistant to B. tabaci biotype B through antixenosis and antibiosis resistance mechanisms.

The level of resistance to late blight Phytophthora infestans (Mont.) de Bary in tomato breeding genotypes in Serbia

Late blight (Phytophthora infestans (Mont.) de Bary) was identified as one of the major diseases causing significant economic losses in tomato production. Thus, the development of resistant cultivars and hybrids was included in tomato breeding programs at the Institute for Vegetable Crops, Smederevska Palanka. A line (S-31), Tomato late blight resistance gene Ph-2 carrier, was diallely crossed with four susceptible lines possessing good production characteristics (S-49, S-31, hom-3 and hom-4) in order to obtain resistant high-yield and quality hybrids. Parental lines and five F1 hybrids, as well as three commercially grown susceptible cultivars (Narvik SPF, Adonis, SP-109, negative control) were tested for resistance toward this pathogen.Sensitivity was evaluated ten days after inoculation on the basis of leaf area necrotic spot, using I to VI level scale. The results imply dominant or partially dominant inheritance pattern. Three commercially grown cultivars were susceptible, as expected. Five of F1 hybrids including S-31 and hom-3 parents were resistant to late blight. The best hybrids were S-31 x hom-3 and S-31 x hom-4 when the morphological traits, yield and resistance were taken into account. Obviously, lines from group hom contributed to increased resistance to tomato late blight with respect to resistant parent. Key words: Inheritance, Ph-2, resistance gene, Solanum lycopersicum.

Fusarium ratings in Ontario winter wheat performance trial (OWWPT) using an index that combines Fusarium head blight symptoms and deoxynivalenol levels

Fusarium head blight (FHB) is one of the most serious diseases of wheat (Triticum aestivum L.). FHB&amp;nbsp;reduces grain yield and quality, and the fungus produces mycotoxins, such as deoxynivalenol (DON). The most practical way to control FHB is through the development of resistant cultivars. In addition to exotic sources of resistance (such as cultivars Sumai 3 and Frontana), native sources of resistance are commonly used in winter wheat breeding programs in North America. In 1996, 2000, and 2004 severe epidemics of FHB cost the winter wheat industry in Ontario, Canada combined over $200 million. All wheat grown in Ontario is entered in the Ontario Winter Wheat Performance Trial (OWWPT) and tested every year for Fusarium resistance and DON&amp;nbsp;level in three inoculated FHB nurseries. The objective of this study is to explain how the index that accounts for FHB&amp;nbsp;symptoms and DON level jointly was developed, and how stable the performance of the cultivars grouped to susceptibility classes has been over a number of years. The index is related to Fusarium susceptibility classes (moderately resistant &amp;ndash; MR, moderately susceptible &amp;ndash; MS, susceptible &amp;ndash; S and highly susceptible &amp;ndash; HS), robust, stable, open-ended (old cultivars out, new cultivars in) and useful to farmers in making cultivars selection decisions. This information is available to growers and industry through the website www.gocereals.ca.

Identification, Genetic Analysis and Mapping of Resistance to Phytophthora sojae of Pm28 in Soybean

Abstract Phytophthora sojae Kanfman and Gerdemann (P. sojae) is one of the most prevalent pathogens and causes Phytophthora root rot, which limits soybean production worldwide. Development of resistant cultivars is a cost-effective approach to controlling this disease. In this study, 127 soybean germplasm were evaluated for their responses to Phytophthora sojae strain Pm28 using the hypocotyl inoculation technique, and 49 were found resistant to the strain. The hypocotyl of Pj, P 2, Fj, and F 23 of two crosses of Ludou 4 (resistant) × Youchu 4 (susceptible) and Cangdou 5 (resistant) × Williams (susceptible) were inoculated with Pm28, and were used to analyze the inheritance of resistance. The population derived from the cross of Ludou 4 × Youchu 4 was used to map the resistance gene (designated as Rps9) to a linkage group. 932 pairs of SSR primers were used to detect polymorphism, and seven SSR markers were mapped near the resistance gene. The results showed that the resistance to Pm28 in Ludou 4 and Cangdou 5 was controlled by a single dominant gene Rps9, which was located on the molecular linkage group N between the SSR markers Satt631 (7.5 cM) and Sat_186 (4.3 cM).

Characterization of genes Rpp2, Rpp4, and Rpp5 for resistance to soybean rust

Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced into soybean plants and for planning breeding strategies against this disease. Here, we infected an F2 population of 140 plants derived from a cross between ‘An-76’, a line carrying two resistance genes (Rpp2 and Rpp4), and ‘Kinoshita’, a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color [LC], frequency of lesions having uredinia [%LU], number of uredinia per lesion [NoU], frequency of open uredinia [%OU], sporulation level [SL], and incubation period [IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters in F2 population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors. Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance.

Powdery mildew resistance in soybean PI 243540 is controlled by a single dominant gene

Powdery mildew (Microsphaera diffusa Cooke &amp; Peck) is a common disease of soybean in many countries of the world, including the northern United States of America and parts of Canada. The genetic resistance of soybean to M. diffusa is known to be controlled by a single locus with three alleles designated as Rmd, Rmd-c and rmd. Identification and characterization of sources of resistance is a prerequisite for the development of resistant cultivars. The objective of this study was to determine the inheritance of powdery mildew resistance in a plant introduction (PI) from Japan, PI 243540. The inheritance of powdery mildew was determined in a segregating population from a cross between powdery mildew susceptible Ohio cultivar Wyandot and PI 243540. The parents and the progeny showed a consistent response to powdery mildew for all growth stages of plants. The two parents, the F1, F2, and F2:3 families from the cross were screened in a greenhouse and field following inoculation with M. diffusa. All F1 plants were resistant to M. diffusa and χ2 analysis for segregation in the population of 343 F2 plants indicated a tight fit for a 3:1 (P = 0.78) ratio, indicative of a single dominant gene. In the next generation, the 334 F2-derived families fit an expected 1 resistant:2 segregating:1 susceptible segregation ratio (P =0.88), which confirmed the results obtained in the F2 generation. Our results indicate that the powdery mildew resistance derived from PI 243540 is controlled by a single dominant gene linked to the Rmd/ Rmd-c/rmd locus. The simple inheritance of this gene should make it relatively easy to find linked DNA markers and transfer the gene to susceptible elite cultivars using the backcross breeding approach.

Molecular and Pathological Characterization of Colletotrichum falcatum Infecting Subtropical Indian Sugarcane

Red rot, caused by Colletotrichum falcatum, is the most significant problem of sugarcane worldwide. Pathological studies and three different marker systems were used to characterize 25 C. falcatum isolates collected from 18 subtropical sugarcane cultivars from 15 different sugarcane-growing regions of three north-eastern states of India to assess pathogen diversity. Of these 25 isolates, three were new (RR2A, RR15, RR83) from cultivars Co 7717, Co J83 and Co S88230, respectively, pathologically characterized on 13 standard differential hosts. Isolates Cf 01, Cf 08 and RR15 were the most, and Cf-07 the least virulent. Molecular characterization using random amplified polymorphic DNA, universal rice primers (URP) and inter simple sequence repeat markers amplified a total of 161 alleles of which 159 were polymorphic (98.76%). Unweighted paired group method with arithmetic averages analysis of combined data of all the DNA markers obtained by three marker systems classified 25 isolates into six clusters at 34% genetic similarity with high Mantel matrix correlation (r = 0.83). The principal component analysis (PCA) of marker data explained 68% of the variation by first three components. Molecular diversity as revealed in these isolates is very high, but non-structured. Isolate Co Pant 84212 was found to be genetically most diverse. We demonstrated for the first time that URPs derived from weed rice could successfully assess genetic diversity in C. falcatum. Molecular characterization of the C. falcatum isolates prevalent in north-eastern India would enable red rot management strategies, selection for resistance genes and development of resistant cultivars.

Susceptibility of Basil Cultivars and Breeding Lines to Downy Mildew (Peronospora belbahrii)

Downy mildew, caused by Peronospora belbahrii, is a new disease of basil (Ocimum spp.) in the United States. In 2009, different basil species, cultivars, and advanced breeding lines of sweet basil (30 in total) were evaluated for susceptibility to basil downy mildew in field trials in southern and northern New Jersey. Popular commercial sweet basil cultivars such as Martina, Nufar, and Poppy Joe were among the most susceptible to downy mildew. Symptoms and sporulation of P. belhahrii on Ocimum ×citriodorum and O. americanum cultivars were present but far less than on most O. basilicum cultivars evaluated. The cultivars Spice, Blue Spice, and Blue Spice Fil were the least susceptible to basil downy mildew with no visible symptoms. Similar results were observed in both field trials. This is the first report of potential resistance in Ocimum spp. to basil downy mildew. Observations from this study show that the development of resistant cultivars may be possible. Selection criteria such as foliar morphology, plant architecture as well as the presence of secondary metabolites are being examined as potential traits for developing downy mildew resistant basil cultivars.

Preparation and epitope characterization of monoclonal antibodies suitable for detection of Tomato yellow leaf curl virus

Tomato yellow leaf curl virus (TYLCV) is a begomovirus that seriously threatens tomato crops worldwide. Current immunodiagnostic methods for this pathogen employ commercially produced mAbs raised against TYLCV. However, despite the existence of these mAbs, little information regarding their characterization or strategy of production has been published. In addition, research on TYLCV would certainly benefit were more mAbs available, thus allowing efficient examination of the virus life cycle, modes of pathogenesis and possibly the development of resistant cultivars. The coat protein (CP) of TYLCV is the only known building block of the viral capsid. Therefore, in this study we used CP as an immunogen for the production of novel mAbs. We employed a strategy in which the CP was truncated at its C-terminus to avoid intra- and inter-protein interactions that could impair epitope exposure. For the same reason, we used a denaturated antigen to expose linear epitopes during the immunization. This effort yielded three mAbs: they were characterized biochemically and immunologically, and their epitopes were mapped. Possible applications of these mAbs are discussed.