BackgroundIn grapevine, as in other fruit crops, fruit size and seed content are key components of yield and quality; however, very few Quantitative Trait Loci (QTLs) for berry weight and seed content (number, weight, and dry matter percentage) have been discovered so far. To identify new stable QTLs for marker-assisted selection and candidate gene identification, we performed simultaneous QTL detection in four mapping populations (seeded or seedless) with various genetic backgrounds.ResultsFor berry weight, we identified five new QTLs, on linkage groups (LGs) 1, 8, 11, 17 and 18, in addition to the known major QTL on LG 18. The QTL with the largest effect explained up to 31% of total variance and was found in two genetically distant populations on LG 17, where it colocalized with a published putative domestication locus. For seed traits, besides the major QTLs on LG 18 previously reported, we found four new QTLs explaining up to 51% of total variance, on LGs 4, 5, 12 and 14. The previously published QTL for seed number on LG 2 was found related in fact to sex. We found colocalizations between seed and berry weight QTLs only for the major QTL on LG 18 in a seedless background, and on LGs 1 and 13 in a seeded background. Candidate genes belonging to the cell number regulator CNR or cytochrome P450 families were found under the berry weight QTLs on LGs 1, 8, and 17. The involvement of these gene families in fruit weight was first described in tomato using a QTL-cloning approach. Several other interesting candidate genes related to cell wall modifications, water import, auxin and ethylene signalling, transcription control, or organ identity were also found under berry weight QTLs.ConclusionWe discovered a total of nine new QTLs for berry weight or seed traits in grapevine, thereby increasing more than twofold the number of reliable QTLs for these traits available for marker assisted selection or candidate gene studies. The lack of colocalization between berry and seed QTLs suggests that these traits may be partly dissociated.
The objective of this work was to evaluate the resistance of 30 Chilean potato landraces to natural infection by Phytophthora infestans during two growing seasons in Southern Chile. Control cultivars were 'Désirée', which has moderate susceptibility to late blight, and 'Karú', which is characterized by moderate resistance to the disease. The response of the potato landraces to late blight infection was assessed weekly by scoring the percentage of foliage destruction during the growing season. Subsequently, the relative area under the disease progress curve (AUDPCr) was calculated. A wide response variation was observed among the landraces during the occurrence of late blight. The comparative analysis of the AUDPCr showed that three landraces achieved high resistance to the disease (low AUDPCr values). These were UCT-34Cor (0.05), UCT-26Ach (0.06) and UCT-27Mu (0.10). Most of the potato landraces were classified into the range moderately resistant to moderately susceptible. The estimated values of heritabilities of the means were moderate to high for the joint analysis of the two years tested (0.65). The wide range of AUDPCr observed within potato landraces suggests the presence of partial resistance in response to the complex virulence pattern of the P. infestans populations present in Southern Chile.
Bulbing was studied in shallot plants cultured in vitro. Bulbing occurred under a 16 h photoperiod with fluorescent + incandescent light and 30-50 g 1(-1) sucrose in the culture medium. Exogenous gibberellin (10 microM GA3) inhibited leaf and root growth and bulbing. When added to the medium at a concentration of 10 microM, three inhibitors of gibberellin biosynthesis (ancymidol, flurprimidol and paclobutrazol) promoted bulb formation and the percentage of bulbing. When ancymidol was used in combination with GA3, it did not reverse the effect of GA3 applied alone. Under treatments with 30-70 g l(-1) sucrose, bulbing ratios greater than those found in control plants were achieved by addition of ancymidol, and bulb fresh weight was increased in the same way. Ancymidol caused a 66% decrease in sucrose content in leaf bases but greatly increased the glucose, fructose and fructan contents. The increase in fructan content by ancymidol could result from the three-fold rise in total [14C]sucrose uptake per plant from the culture medium associated with a marked increase in leaf base labelling at the expense of root labelling. The possible role of ancymidol is discussed and evidence supports a major regulatory role for gibberellins in bulbing.
Background:The object of this work was to determine the genetic and allelic diversity of Solanum species present in Chile, assessing allelic distribution among native varieties and commercial cultivars of Solanum tuberosum ssp. tuberosum L., using microsatellite markers. Results: A high level of allelic richness was found in the potatoes studied. The seven microsatellite markers used presented a total of 64 allelic variants among native varieties and commercial cultivars of Solanum tuberosum ssp. tuberosum. The SSR loci generated an average of 9.16 alleles/locus. The group with the highest PIC was that of native varieties collected in the Chiloe archipelago. The high PIC values found indicate that the native varieties from Chiloe have a low level of interrelation, representing wide genetic diversity. Conclusions:The markers with the highest number of alleles in native varieties corresponded to loci STG 0016 and LEMALX. Commercial cultivars do not present the same genetic variability as native varieties, and the allelic richness of commercial cultivars is lower than that of native varieties of S. tuberosum ssp. tuberosum. Most of the native varieties were clustered in accordance with their geographical location, while commercial cultivars, were clustered in accordance with their breeding programs in Chile and Europe, with the exception of Shepody.
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