Uncovering tomato candidate genes associated with drought tolerance using Solanum pennellii introgression lines.

Tomato plants are sensitive to drought stress throughout their growth cycle. To be considered drought-tolerant, a cultivar should display tolerance at all developmental stages. This study aimed to evaluate whether Solanum pennellii introgression lines (ILs) previously selected as drought-tolerant during germination/seedling growth maintained this tolerance in the vegetative/reproductive stage. We then investigated these ILs to uncover candidate genes. The plants were subjected to two different environmental conditions: well-watered and drought-stressed (water withheld for ≤ 20 d after flowering). Phenotyping for morphological, physiological, fruit quality, and yield-related traits was performed, and the data was analyzed using a mixed-model approach. Using a multi-trait index that relies on factor analysis and genotype-ideotype distance (FAI-BLUP index), the genotypes were ordered based on how far they were from the drought-tolerant ideotype. Afterward, the tomato IL population map furnished by the SOL Genomics Network was utilized to identify introgressed segments of significance for the identification of candidate genes. Significant genotypic differences were found in the yield, water content, mean weight, length, and width of the fruit, the percentage of fruits displaying blossom-end rot, and titratable acidity. The drought-tolerance ideotype was built considering the maximum values for the fruit water content, number of fruits, mean fruit weight, and yield, minimum values for blossom-end rot, and mean values for titratable acidity. IL 1-4-18, IL 7-4-1, IL 7-1, IL 7-5-5, and IL 1-2 were ranked above M-82 and therefore considered drought-tolerant during the vegetative/reproductive stage. IL 1-4-18 and IL1-2 sustained drought tolerance displayed during germination/seedling growth into the vegetative/reproductive stage. The following candidate genes associated with drought tolerance were identified: AHG2, At1g55840, PRXIIF, SAP5, REF4-RELATED 1, PRXQ, CFS1, LCD, CCD1, and SCS. Because they are already associated with genetic markers, they can be transferred to elite tomato cultivars through marker-assisted technology after validation.

Hydroxy proline and gamma-aminobutyric acid: markers of susceptibility to vine decline disease caused by the fungus Monosporascus cannonballus in melons (Cucumis melo L.).

Background: Vine decline disease caused by the fungus Monosporascus cannonballus, is a threat to melon production (Cucumis melo L.) worldwide. Nonetheless, little is known about the metabolites produced during the host pathogen interaction. Thus, the objective of this study was to measure quantities of amino acids produced over time during such an interaction. Methods: Two melon genotypes named TAM-Uvalde (susceptible) and USDA PI 124104 (resistant) were grown and inoculated with M. cannonballus. The metabolites previously stated were measured before inoculation (0 hours) and 24, 48 and 72 hours after inoculation, using high performance liquid chromatography analysis. Results: The production of some amino acids during the interaction of the resistant and susceptible melon genotypes with the fungus M. cannonballus was different regarding quantities over time. Interestingly, hydroxy proline was always up-regulated in higher quantities in response to pathogen infection in the genotype TAM-Uvalde. Also, the up-regulation in higher quantities of gamma-aminobutyric acid in the genotype TAM-Uvalde 48 and 72 hours after inoculation, suggests more penetration of the pathogen in its roots. Hence, taken together, hydroxy proline and gamma-aminobutyric acid levels could be used as markers of susceptibility to vine decline disease caused by M. cannonballus, which could be useful in developing resistant varieties.

Evaluation of anatomical and physiological traits of Solanum pennellii Cor. associated with plant yield in tomato plants under water-limited conditions.

Although intensively studied, few works had looked into S. pennellii's ability to cope with water-deficit conditions from a breeding point of view. In this study, we assessed potential traits of S. pennellii, that had previously been linked to high yields in other plant species, under long-term water-limited conditions and made a parallel with plant yield. For this purpose, the drought-resistant tomato genotypes IL 3-5 and IL 10-1, and the drought-sensitive IL 2-5 and IL 7-1 at seed level, together with both parents the S. pennellii accession LA 716 and the cultivar M82 were kept at 50 and 100% ASW throughout the growing season. Our findings confirm the superiority of LA 716 under water-limited conditions compared to the other S. lycopersicum genotypes in terms of plant water status maintenance. Percentual reduction on plant yield was higher in IL 3-5 and IL 10-1 than in M82 plants, indicating no correlation between drought resistance on germination and plant productive stages. A strong positive correlation was found between fruit yield and A, gs, and Ψleaf at 50% ASW, suggesting these traits as important selection criteria. LT and gmin, LA 716's most promising traits, did not show a linear correlation with fruit yield under low water regimes. This study unravels traits behind tomato performance under water-limited conditions and should work as guidance for breeders aiming at developing drought-resistant tomato cultivars.

Resistance of the wild tomato Solanum habrochaites to Phytophthora infestans is governed by a major gene and polygenes.

This work aimed to study the inheritance of resistance to Phytophthora infestans in tomato plants, using the maximum likelihood estimation function. The susceptible cultivar Santa Clara (Solanum lycopersicum) was used as the female genitor and the P. infestans resistant S. habrochaites f. glabratum accession (BGH 6902) as the male genitor. F1 plants from the crossing were self-pollinated to produce F2 progenies, and also backcrossed with PR and PS to produce BC1:R and BC1:S generations, respectively. The tomato plants were inoculated 50 days after transplanting. Disease severity was evaluated via a diagrammatic scale. Comparison of the genetic models created using the maximum likelihood function revealed that the inheritance of resistance to P. infestans in S. habrochaites is conferred by a major gene with additive and dominance effects, polygenes with additive effects, plus the environmental effect. Vertical resistance can be explored using genes with major effects. Programs of recurrent and maker-assisted selection are considered efficient strategies with which to select genotypes that hold P. infestans resistance conferred by polygenes.