Margarita Lema

Inheritance of White Mold Resistance in Phaseolus vulgaris × P. coccineus Crosses

The fungus Sclerotinia sclerotiorum, cause of white mold, is known to attack >400 plant species. It is a widespread problem in dry bean (Phaseolus vulgaris) in the United States, causing >30% average yield losses. Low to moderate levels of resistance are found in dry bean. However, some accessions of P. coccineus (commonly known as scarlet runner bean) possess a relatively higher level of resistance. Our objective was to verify the reaction of 13 known white mold-resistant P. coccineus germ plasms and determine inheritance of resistance in accessions PI 433246 and PI 439534. Pinto Othello was crossed with PI 433246, and the resulting interspecific F1 was back-crossed onto Othello and allowed to produce F2 seed. Similarly, pinto UI 320 was crossed with PI 439534. The F1 was backcrossed onto UI 320 and allowed to produce F2 seed. The two parents, F1, F2, and backcross to dry bean of each set were evaluated in the greenhouse using the straw test at Fort Collins, CO in 2004. All 13 P. coccineus accessions and the two F2 also were evaluated using the modified petiole test at Kimberly, ID in 2005. All 13 P. coccineus accessions were variable in a 2002 straw test when rated for white mold reaction on a 1-to-9 scale, because the mean disease score ranged from 1.9 for PI 433246 to 4.4 for PI 189023 and 8.8 for the susceptible check Bill Z. For the petiole test, when rated on a 1-to-9 scale, the accessions exhibited an intermediate white mold score of 4 or 5 in 2005. In 2004, the susceptible check Othello exhibited a mean score of 7.9 compared with 3.4, 3.2, and 2.1 for PI 433246, UI 320, and PI 439534, respectively. The white mold reaction of PI 433246 and PI 439534 was dominant in their respective F1. The F2 segregation further indicated that white mold resistance in PI 433246 and PI 439534 was controlled by a single dominant gene. These two and other white mold-resistant P. coccineus accessions and selected breeding lines from the interspecific crosses should be useful for future improvement of white mold resistance of pinto and other market classes of dry and green or snap bean.

In Vitro Activity of Glucosinolates and Their Degradation Products against Brassica-Pathogenic Bacteria and Fungi

ABSTRACT Glucosinolates (GSLs) are secondary metabolites found in Brassica vegetables that confer on them resistance against pests and diseases. Both GSLs and glucosinolate hydrolysis products (GHPs) have shown positive effects in reducing soil pathogens. Information about their in vitro biocide effects is scarce, but previous studies have shown sinigrin GSLs and their associated allyl isothiocyanate (AITC) to be soil biocides. The objective of this work was to evaluate the biocide effects of 17 GSLs and GHPs and of leaf methanolic extracts of different GSL-enriched Brassica crops on suppressing in vitro growth of two bacterial (Xanthomonas campestris pv. campestris and Pseudomonas syringae pv. maculicola) and two fungal (Alternaria brassicae and Sclerotinia scletoriorum) Brassica pathogens. GSLs, GHPs, and methanolic leaf extracts inhibited the development of the pathogens tested compared to the control, and the effect was dose dependent. Furthermore, the biocide effects of the different compounds studied were dependent on the species and race of the pathogen. These results indicate that GSLs and their GHPs, as well as extracts of different Brassica species, have potential to inhibit pathogen growth and offer new opportunities to study the use of Brassica crops in biofumigation for the control of multiple diseases.

Effect of regeneration procedures on the genetic integrity of Brassica oleracea accessions

A Brassica oleracea collection of landraces collected in the northwest of Spain is kept at the Gene Bank placed at ‘Misión Biológica de Galicia’. Landraces of the collection are regenerated from time to time to restore the viability of the seed and to carry on field trials. The objective of this work is to study the effect of regeneration on the genetic integrity of three accessions of this collection, and to investigate the possible causes of the genetic changes observed. After characterizing the original populations and their following regenerated populations by 25 SSRs we concluded that there were significant changes in the population structure and the allelic frequency of individual loci due to the action of genetic drift, directional selection and probably assortative mating. Protocols to store and regenerate the accessions should be improved in order to avoid the effect of these forces in the genetic integrity of the collection.

Assessment of runner bean ( Phaseolus coccineus L.) germplasm for tolerance to low temperature during early seedling growth

The runner bean requires moderately high temperatures for optimum germination and growth. Low temperature at sowing delays both germination and plant emergence, and can reduce establishment of beans planted early in the growing season. The objective of this work was to identify potential runner bean germplasm with tolerance to low temperature and to assess the role of this germplasm for production and breeding. Seeds of 33 runner bean accessions were germinated in a climate-controlled chamber at optimal (17°C-day/15°C-night) and at sub-optimal (14°C-day/8°C-night) temperature. The low temperature tolerance was evaluated on the basis of germination, earliness, ability to grow and vigor. Differences in agronomical characters were significant at low temperatures for germination, earliness, ability to grow and early vigor except for emergence score. The commercial cultivars Painted Lady Bi-color, Scarlet Emperor, the Rwanda cultivar NI-15c, and the Spanish cultivars PHA-0013, PHA-0133, PHA-0311, PHA-0664, and PHA-1025 had the best performance under cold conditions.

Discrimination of Xanthomonas campestris pv. campestris races among strains from northwestern Spain by Brassica spp. genotypes and rep-PCR

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) is a severe seedborne disease of Brassica crops around the world. Nine races are recognized, being races 1 and 4 the most aggressive and widespread. The identification of Xcc races affecting Brassica crops in a target area is necessary to establish adequate control measures and breeding strategies. The objectives of this study were to isolate and identify Xcc strains from northwestern Spain by using semi-selective medium and pathogenicity tests, determine the existing races of Xcc in this area by differential series of Brassica spp., and evaluate the use of repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR) to differentiate among the nine existing Xcc races. Seventy five isolates recovered from infected fields were identified as Xcc. Race-typing tests determined the presence of the following seven pathogen races: 1, 4, 5, 6, 7, 8 and 9. Race 4 was the most frequent in Brassica oleracea and race 6 in Brassica rapa crops, therefore breeding should be focussed in obtaining resistant varieties to both races. Cluster analysis derived from the combined fingerprints showed four groups, but no clear relationship to race, crop or geographical origin was found. Rep-PCR analysis was found not to be a reliable method to discriminate among Xcc races, therefore race typing of Xcc isolates should be done by using the differential series of Brassica spp. genotypes or another alternative approach.

Resistance of Cabbage (Brassica oleracea capitata Group) Crops to Mamestra brassicae

ABSTRACT Twenty-one cabbage (Brassica oleracea capitata group) varieties, including 16 local varieties and five commercial hybrids, were screened for resistance to the moth Mamestra brassicae L. under natural and artificial conditions in northwestern Spain. Resistance was assessed as the proportion of damaged plants and damaged leaves, leaf feeding injury, and number of larvae present. Correlation coefficients among damage traits showed that a visual scale (general appearance rating) should be a useful indicator of resistance. Most local varieties were highly susceptible to M. brassicae, whereas the commercial hybrids tested were resistant in terms of head foliage consumption and number of larvae per plant. Performance of varieties was similar under natural and artificial infestation although some of them performed differently at each year. Three local varieties (MBG-BRS0057, MBG-BRS0074, and MBG-BRS0452) were highly susceptible at both natural and artificial infestation conditions being MBG-BRS0074 the most damaged variety. Two local varieties (MBG-BRS0402 and MBG-BRS0535) and commercial hybrids were identified as resistant or moderately resistant to M. brassicae. Among them, ‘Corazon de Buey’ and ‘Cabeza negra’ were the most resistant and produced compact heads. These varieties could be useful sources of resistance to obtain resistant varieties to M. brassicae or as donors of resistance to other Brassica crops. The possible role of leaf traits, head compactness, and leaf glucosinolate content in relation to M. brassicae resistance is discussed.

In Vivo and in Vitro Effects of Secondary Metabolites against Xanthomonas campestris pv. campestris

Brassica rapa is a crucifer that is grown worldwide, mainly as a vegetable. The quality of B. rapa crops is highly affected by the disease caused by the bacteria Xanthomonas campestris pv. campestris (Xcc). Glucosinolates and phenolic compounds can confer resistance to Brassica crops against pests and diseases, but few works have been done to evaluate their role in Xcc resistance. The objectives of this work were: (1) to evaluate the in vivo and in vitro antibacterial effect of gluconapin, its isothiocyanate and the methanolic extracts of B. rapa against the type 4 of Xcc, and (2) to test if there is induced resistance mediated by glucosinolates or phenolic compounds in two varieties of B. rapa. Gluconapin and its ITC varieties had an antibacterial effect on the development of Xanthomonas and this effect was strongly dependent on the concentration applied. Methanolic extracts from B. rapa, containing glucosinolates and phenolic compounds, inhibited the growth of these bacteria. Concentration of gluconapin is higher in resistant plants than in the susceptible ones and there is an induction of gluconapin, some flavonoids and sinapic acid 48 to 72 h after inoculation. Gluconapin plays a role in the constitutive resistance to Xcc, while gluconapin, some flavonoids and hydroxycinnamic acids are induced by a Xcc infection but it is not clear if this induction confers resistance to this disease.

Genetic structure and diversity of a collection of Brassica rapa subsp. rapa L. revealed by simple sequence repeat markers

This research was supported by project RF-2006-00028-00-00 and the Excma. Diputacion Provincial de Pontevedra, Spain.

Genotypic and Environmental Effects on Agronomic and Nutritional Value of Brassica rapa

Research supported by the the Xunta de Galicia (PGIDIT06RAG40302PR), the Plan Nacional I+D+I (AGL2009-09922) and the Excma. Diputacion Provincial de Pontevedra. Marta Francisco acknowledges an I3P fellowship from the CSIC.

Identification of Sources of Resistance to Xanthomonas campestris pv. campestris in Brassica napus Crops

Research was supported by the project AGL2009-09922 and Excma. Diputacion Provincial de PontevedraBlack rot, caused by Xanthomonas campestris pv. campestris, is one of the most important diseases affecting Brassica crops worldwide. Nine races have been differentiated in X. campestris pv. campestris, with races 1 and 4 being the most virulent and widespread. The objective of this work was to identify sources of resistance to races 1 and 4 of X. campestris pv. campestris in different Brassica napus crops, mainly in the underexplored pabularia group. Seventy-six accessions belonging to four B. napus groups were screened for resistance to two X. campestris pv. campestris races (1 and 4). The strain of race 1 used in this study was more virulent on the tested materials than the strain of race 4. No race-specific resistance was found to race 1. Most cultivars were susceptible except Russian kale, from the pabularia group, which showed some resistant plants and some other accessions with some partially resistant plants. High levels of race-specific resistance to race 4 were found in the pabularia group, and great variability within accessions was identified. Three improved cultivars (Ragged Jack kale, Friese Gele, and Valle del Oro) and four landraces (Russian kale, MBG-BRS0037, MBG-BRS0041, and MBG-BRS0131) showed plants with some degree of resistance to both races, which may indicate that race-nonspecific resistance is involved. These accessions could be directly used in breeding programs, either as improved cultivars or as donors of race-specific resistance to other Brassica cultivars.