Good seedling establishment is essential for crop production to be both resource efficient and cost effective and is therefore widely accepted as a critically important trait for farmers. Successful crop establishment is dependent on high seed vigour (Finch-Savage, 1995), but despite improvements over the years by seed producers, this aspect of seed quality remains illusive. Seed vigour is greatly influenced by seed production and storage environment, but also has an important genetic basis (Bettey et al., 2000). Until now, technological solutions (e.g. improved seedbeds, seed selection and treatment) have been used to improve establishment, by tackling the negative effects of seed production and storage environments, but it remains variable. Recent developments in genetic resources now provide the opportunity to identify key seed vigour genes through a trait-led approach for use in breeding programmes and the development of seed vigour testing to help solve this perennial problem. The identification of these genes not only provides these practical benefits, but also provides the opportunity to develop a scientific understanding of the basis of seed vigour differences that is currently lacking.
Trait identification: In extensive field crop studies and the development of predictive seedling establishment models (e.g. Finch-Savage et al. 1993, 1998, 2001, 2005a; Rowse and Finch-Savage, 2002; Whalley et al. 1999) we have identified three key features the seed/seedling must possess to establish well across a wide range of seedbed conditions and which are therefore key elements of seed vigour. The seed must: 1, germinate rapidly; 2, have rapid initial downward growth to maintain contact with moisture in a drying seed bed; and 3, have high potential for upward shoot growth in soil of increasing impedance as the soil dries. All these features reduce the time between sowing and seedling emergence when the seed bed deteriorates negatively impacting on establishment (Finch-Savage et al., 1993, 1998).
QTL analysis and fine mapping: We have identified significant QTL for each of the three seed vigour components described above (Bettey et al. 2000; Finch-Savage et al. 2005) through screening a population of B. oleracea doubled haploid (DH) lines produced from a cross between DH parents of a rapid cycling Chinese kale var. alboglabra (A12DHd) and a calabrese var. italica (GDDH33). We have confirmed a number of these QTL in a second DH population (cauliflower CA25 (var. botrytis) X sprout AC498 (var. gemmifera)) and further confirmation was obtained using substitution lines. Two QTL for the rate of germination trait were found on linkage groups BoLGO1 and BoLGO3 (Rate of Germination ROG1 and 2 respectively). We have fine mapped ROG1 using informative lines from a backcross substitution library. One substitution line (SL101) was identified that had a small introgressed region (1-9 cM), from the fast germinating GDDH33 parent in the slow germinating reference background parent A12DHd. This was found to be at the telomeric end of BoLGO1. This introgression accounted for much of the difference in germination rate between the parent lines (see physiological characterisation below). Subsequent work has allowed us to show that the introgression defining the now “Mendelised” QTL ROG1 is nearer to 1cM.
Work is now underway to identify the gene/s underlying this trait and to look for an association between allelic and phenotypic variation in Brassica oleracea. To this end we have just been awarded a BBSRC grant from their recent Crop Science Initiative “A trait-led approach which exploits natural variation in seed vigour to enhance crop establishment”
Brassica Oleracea Crop Types