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

Addressing the threat of climate change to agriculture requires improving crop resilience to short-term abiotic stress

Climate change represents a serious threat to global agriculture, necessitating the development of more environmentally resilient crops to safeguard the future of food production. The effects of climate change are appearing to include a higher frequency of extreme weather events and increased day-to-day weather variability. As such, crops which are able to cope with short-term environmental stress, in addition to those that are tolerant to longer term stress conditions are required . It is becoming apparent that the hitherto relatively little studied process of post-stress plant recovery could be key to optimizing growth and production under fluctuating conditions with intermittent transient stress events. Developing more durable crops requires the provision of genetic resources to identify useful traits through the development of screening protocols. Such traits can then become the objective of crop breeding programmes. In this study, we discuss these issues and outline example research in leafy vegetables that is investigating resilience to short-term abiotic stress

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