Analysis of Brassica oleracea early stage abiotic stress responses reveals tolerance in multiple crop types and for multiple sources of stress

BACKGROUND Brassica oleracea includes a number of important crop types such as cabbage, cauliflower, broccoli and kale. Current climate conditions and weather patterns are causing significant losses in these crops, meaning that new cultivars with improved tolerance of one or more abiotic stress types must be sought. In this study, genetically fixed B. oleracea lines belonging to a Diversity Fixed Foundation Set (DFFS) were assayed for their response to seedling stage-imposed drought, flood, salinity, heat and cold stress. RESULTS Significant (P ≤ 0.05) variation in stress tolerance response was found for each stress, for each of four measured variables (relative fresh weight, relative dry weight, relative leaf number and relative plant height). Lines tolerant to multiple stresses were found to belong to several different crop types. There was no overall correlation between the responses to the different stresses. CONCLUSION Abiotic stress tolerance was identified in multiple B. oleracea crop types, with some lines exhibiting resistance to multiple stresses. For each stress, no one crop type appeared significantly more or less tolerant than others. The results are promising for the development of more environmentally robust lines of different B. oleracea crops by identifying tolerant material and highlighting the relationship between responses to different stresses. © 2017 Society of Chemical Industr

Quantitative trait loci (QTLs) linked with root growth in lettuce (Lactuca sativa) seedlings

In-field variation of transplanted lettuce (Lactuca sativa L.) due to variable soil and environmental conditions is one of the major restrictions in the optimization of production and yield. Marker-assisted breeding for lettuce varieties with a more rapid rooting phenotype has the potential to improve the performance of lettuce transplants. This study aimed to identify traits linked with increased primary root length, lateral root length and lateral root emergence in 14-day L. sativa seedlings from an intra-specific cross (Saladin × Iceberg). In total, 16 significant quantitative trait loci (QTLs) were associated with increased root growth traits that would allow direct introgression of the traits. Six of the QTLs were associated with increased primary root growth, accounting for 60.2% of the genetic variation for the trait. Three QTLs were associated with lateral root growth (38.6% of genetic variation); two QTLs were associated with lateral root length density (27.6% of genetic variation) and three with root number density (33.4% of genetic variation), and two QTLs were associated with mean lateral root length (21.1% of genetic variation). The statistical QTLs were located across 9 different linkage groups (LGs) representing loci on 7 of the 9 L. sativa chromosomes. A combination of restriction fragment length polymorphism (RFLPs) and Kompetitive allele specific PCR (KASPs) markers linked to these rooting traits were identified, which could allow breeders to select for a rapid establishment phenotype

Tipburn resilience in lettuce (Lactuca spp.) – the importance of germplasm resources and production system‐specific assays

BACKGROUND Tipburn is a physiological disorder of lettuce (Lactuca spp.). It causes discoloration and collapse of leaf margins, leading to unsaleable crops in both protected (glasshouse, hydroponic) and outdoor production systems. The occurrence of tipburn is hard to predict and is sensitive to environmental conditions. Phenotyping for tipburn resilience requires diverse germplasm resources and, to date, limited material has been investigated for this condition. RESULTS Using a Lactuca diversity fixed foundation set (DFFS) under glasshouse conditions, we identified a significant (P < 0.001) genotypic effect on tipburn resilience across both the entire population and across lines belonging to the cultivated species L. sativa alone. Latuca sativa lines exhibited significantly (P < 0.05) higher average tipburn severity than those belonging to the wild species L. saligna, L. serriola, and L. virosa but we were able to identify both cultivated and wild tipburn-resilient lines. Leaf morphology factors, which included pigmentation, width, and serration, also significantly (P < 0.05) influenced tipburn resilience. Using a recombinant inbred line (RIL) mapping population derived from two DFFS lines, different small-effect quantitative trait loci (QTLs) accounting for 12.3% and 25.2% of total tipburn variation were identified in glasshouse and field conditions, respectively. CONCLUSIONS These results reflect the advantages of phenotyping under production-system-specific conditions for the examination of environmentally sensitive traits and highlight genetic markers and germplasm resources for the development of tipburn resilient lines for use in both protected and outdoor lettuce production

Assembly and characterisation of a unique onion diversity set identifies resistance to Fusarium basal rot and improved seedling vigour

Conserving biodiversity is critical for safeguarding future crop production. Onion (Allium cepa L.) is a globally important crop with a very large (16 Gb per 1C) genome which has not been sequenced. While onions are self-fertile, they suffer from severe inbreeding depression and as such are highly heterozygous as a result of out-crossing. Bulb formation is driven by daylength, and accessions are adapted to the local photoperiod. Onion seed is often directly sown in the field, and hence seedling establishment is a critical trait for production. Furthermore, onion yield losses regularly occur worldwide due to Fusarium basal rot caused by Fusarium oxysporum f. sp. cepae. A globally relevant onion diversity set, consisting of 10 half-sib families for each of 95 accessions, was assembled and genotyping carried out using 892 SNP markers. A moderate level of heterozygosity (30–35%) was observed, reflecting the outbreeding nature of the crop. Using inferred phylogenies, population structure and principal component analyses, most accessions grouped according to local daylength. A high level of intra-accession diversity was observed, but this was less than inter-accession diversity. Accessions with strong basal rot resistance and increased seedling vigour were identified along with associated markers, confirming the utility of the diversity set for discovering beneficial traits. The onion diversity set and associated trait data therefore provide a valuable resource for future germplasm selection and onion breeding

The evolutionary history of wild, domesticated, and feral brassica oleracea (Brassicaceae)

Understanding the evolutionary history of crops, including identifying wild relatives, helps to provide insight for conservation and crop breeding efforts. Cultivated Brassica oleracea has intrigued researchers for centuries due to its wide diversity in forms, which include cabbage, broccoli, cauliflower, kale, kohlrabi, and Brussels sprouts. Yet, the evolutionary history of this species remains understudied. With such different vegetables produced from a single species, B. oleracea is a model organism for understanding the power of artificial selection. Persistent challenges in the study of B. oleracea include conflicting hypotheses regarding domestication and the identity of the closest living wild relative. Using newly generated RNA-seq data for a diversity panel of 224 accessions, which represents 14 different B. oleracea crop types and nine potential wild progenitor species, we integrate phylogenetic and population genetic techniques with ecological niche modeling, archaeological, and literary evidence to examine relationships among cultivars and wild relatives to clarify the origin of this horticulturally important species. Our analyses point to the Aegean endemic B. cretica as the closest living relative of cultivated B. oleracea, supporting an origin of cultivation in the Eastern Mediterranean region. Additionally, we identify several feral lineages, suggesting that cultivated plants of this species can revert to a wild-like state with relative ease. By expanding our understanding of the evolutionary history in B. oleracea, these results contribute to a growing body of knowledge on crop domestication that will facilitate continued breeding efforts including adaptation to changing environmental conditions

Cultivar-level genotype differences influence diversity and composition of lettuce (Lactuca sp.) phyllosphere fungal communities

Different lettuce genotypes supported significantly different phyllosphere fungal communities. Phyllosphere fungal diversity was low and fungi fell into five similarity groups. These groups were represented in significantly different proportions throughout 26 lettuce accessions indicating cultivar-level variation in the fungal colonization of the lettuce phyllosphere. Significant differences in the proportions of the two dominant groups (with similarity to Cladosporium spp. and Sporobolomyces roseus) were identified between parental lines of two lettuce mapping populations providing opportunities to further investigate the genetic control of cultivar-level variation in fungal phyllosphere colonisation