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Cucurbita maxima Duchesne squash and pumpkins are cultivated world-wide. Cucurbita maxima fruits are produced for fresh market and are valuable for food processing. Therefore, fruit characteristics and yield are the traits of high economic importance for breeders. To date, the genetic basis of fruit-associated traits in C. maxima have been poorly understood. In the present study, we evaluated fruit-associated traits and conducted quantitative trait locus (QTL) analysis using recombinant inbred lines (RILs) derived from a cross of two inbred lines with different fruit morphotypes. Phenotypic data for nine fruit traits (earliness, weight, number per plant, yield per plant, length and diameter, shape index, flesh thickness, sucrose content and dry matter content) were collected for RILs in two open-field experiments. Pairwise analysis of the phenotypic data revealed correlations among the fruit and yield-associated traits. Using a previously developed genetic map, we identified 26 QTLs for eight traits. The QTLs were found in 10 locations on eight chromosomes of C. maxima. The QTLs were detected across experiments and explained up to 41.4% of the observed phenotypic variations. Major-effect QTLs for multiple fruit-associated traits were clustered on chromosome 4, suggesting that this genomic region has been under selection during diversification and/or domestication of C. maxima.

The high content of carotenoids, sugars, dry matter, vitamins and minerals makes the fruit of winter squash (Cucurbita maxima Duchesne) a valuable fresh-market vegetable and an interesting material for the food industry. Due to their nutritional value, long shelf-life and health protective properties, winter squash fruits have gained increased interest from researchers in recent years. Despite these advantages, the genetic and genomic resources available for C. maxima are still limited. The aim of this study was to use the genetic mapping approach to map the ovary colour locus and to identify the quantitative trait loci (QTLs) for high carotenoid content and flesh colour. An F6 recombinant inbred line (RIL) mapping population was developed and used for evaluations of ovary colour, carotenoid content and fruit flesh colour. SSR markers and DArTseq genotyping-by-sequencing were used to construct an advanced genetic map that consisted of 1824 molecular markers distributed across linkage groups corresponding to 20 chromosomes of C. maxima. Total map length was 2208 cM and the average distance between markers was 1.21 cM. The locus affecting ovary colour was mapped at the end of chromosome 14. The identified QTLs for carotenoid content in the fruit and fruit flesh colour shared locations on chromosomes 2, 4 and 14. QTLs on chromosomes 2 and 4 were the most meaningful. A correlation was clearly confirmed between fruit flesh colour as described by the chroma value and carotenoid content in the fruit. A high-density genetic map of C. maxima with mapped loci for important fruit quality traits is a valuable resource for winter squash improvement programmes.Electronic supplementary materialThe online version of this article (10.1007/s11032-018-0869-z) contains supplementary material, which is available to authorized users.

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The present work compiles the results of three-year expeditions organized between 2011 and 2013 aimed at plant crop collection in the area of Lithuania, an Eastern European country. Accessions of fruit trees, vegetables, cereals, forage, industrial, fibrous, medical, and spice crops as well as accompanying segetal plants were collected in 5 ethnographic regions of Lithuania. In total, 1010 samples of seeds, bulbs, and plant grafts were obtained. The majority of the collected samples belonged to the Cucurbitaceae, Fabaceae, Solanaceae, Alliaceae, and Rosaceae families. The accessions were described and deposited in the long-term storage in Lithuanian and Polish Gene Banks. Almost all collected cucumbers, pumpkins, squashes, and oat plants were morphologically characterized in field experiments. Cucurbita pepo accessions showed high morphological diversity, while limited diversity of cucumber accessions was observed. Oat plants were characterized by high morphological diversity and resistance to diseases present in some of the investigated accessions. Further characterization of collected apple trees and other accessions is underway. Obtaining germplasm in the area of Lithuania fulfills a gap in current plant crop collections. Collected material could be valuable for pre-breeding evaluation and further breeding programs as well as the study of genetic diversity.