Juan J. Ruiz

Widening the genetic basis of virus resistance in tomato

Abstract New and old accessions of Lycopersicon chilense (LA 1932, LA 1938 and LA 1963), L. peruvianum (PI-143679 and PI-126944), and L. hirsutum (UPV-16910) recently reported as resistant to TSWV, TYLCV and PepMV, viral agents responsible for the most severe economic losses in tomato crop in Spain, were selected as male parents for crosses with L. esculentum in order to widen the genetic basis of virus resistance in tomato. After the analysis of the nature and severity of the barriers found in each case, crossability barriers between wild and cultivated species were circumvented by using several techniques. Crosses with pollen mixture (1:1, wild:cultivated) were successful in obtaining interspecific hybrids with the two L. chilense accessions (LA 1932 and LA 1963) that exhibited more relaxed post-cigotic barriers. Embryo rescue was also successful in crosses with these accessions and also in crosses with L. peruvianum accessions in which embryos beyond the globular stage were found (PI-143679). However, a combination of two or more strategies was necessary in crosses with those accessions exhibiting more severe crossability barriers. Mixture pollen crosses (10:1, wild:cultivated), combined with embryo rescue, allowed for the recovery of hybrids with LA 1938. Stigma and pistil complementation with H 3 BO 3 and GA 3 , followed by immature seed culture was found to be an effective method for the production of novel interspecific hybrids with PI-126944, the accession with the highest level of resistance to TSWV and TYLCV. By using the best combination of techniques we also backcrossed these interspecific hybrids to tomato to generate the BC1 progeny. The new genes introgressed will be useful to obtain new tomato varieties resistant to TSWV, TYLCV and PepMV.

The pepino (Solanum muricatum, Solanaceae): a "new" crop with a history

Pepino,Solanum muricatum, is an herbaceous subshrub that has long been grown in its native Andean South America. Pepino is usually cultivated for its edible fruits, but also has other economic uses. In spite of being a prominent crop in prehispanic times in the Andes, interest in pepino was cast into oblivion from some decades after the Spanish arrival to the present. Pepino etymology, prehispanic distribution, and postcolumbian dispersal are presented, with emphasis on outstanding historical aspects. Speculations on why the pepino has been neglected are also given. These include some features of pepino itself together with misconceptions. However, the pepino is today a species of increasing economic interest, and has a considerable potential for future exploitation.ResumenEl pepino dulce (Solanum muricatum),es una planta herbácea que ha sido cultivada durante mucho tiempo en los Andes, su zona de origen. El pepino dulce normalmente se cultiva por sus frutos comestibles, aunque también tiene otros usos de importancia económica. A pesar de ser un cultivo importante en la zona andina durante la época precolombina, desde unas décadas después de la llegada de los españoles en adelante, el interés por el pepino dulce cayé en el olvido. En este artículo se presentan la etimología, distribución en la época precolombina y su difusión postcolombina, haciendo particular énfasis en los aspectos históricos más destacados. También se dan algunas razones que podrían haber tenido influencia para marginar al pepino dulce. Entre éstas se incluyen algunas carícterísticas propias del pepino dulce junto con falsas creencias. Sin embargo, en la actualidad, el pepino dulce es una planta con un interés económico creciente y con un potencial considerable para su explotación en el futuro.

Diversity and structure of a sample of traditional Italian and Spanish tomato accessions

Italy and Spain are the countries with the oldest record of tomato cultivation in Europe and arguably, with the higher number of traditional and heirloom varieties. In this work we evaluated the genetic diversity and structure in a sample of 26 cultivated accessions belonging to four traditional tomato types, Muchamiel and De la Pera from Spain, and San Marzano and Sorrento from Italy. The (GATA)4 fingerprinting of the 109 genotypes confirmed the ability of this DNA marker to discriminate tomato plants that are otherwise difficult to distinguish. Furthermore, both the estimated population structure and the genetic differentiation statistics were consistent in indicating that subpopulations are more likely to correspond to farmers’ breeding efforts and market specialization than to country-specific groups. Our results provide useful information not only for germplasm description and management but also for current breeding programs in both regions.

Variation in carbohydrate content during ripening in two clones of pepino

Fruits from pepino (Solanum muricatum Aiton) clones ‘Sweet Long’ and ‘Sweet Round’ were harvested at three stages of ripeness (green, turning and ripe). Changes in the carbohydrate fraction (total and free sugars, soluble and insoluble fibre) during on-bush ripening were evaluated in an early and a late crop in the autumn–winter cycle. Significant differences in composition were found for the effects of clone, crop and their interaction. This indicates that there is a considerable variation in the physiology of ripening. We found that total carbohydrate content was on average higher in ‘Sweet Long’ than in ‘Sweet Round’ and higher in the late crop than in the early one. Crossover interaction was detected for sugar content in the two clones, so that in the late crop the clone with highest sugar content was ‘Sweet Long’ while in the early crop it was ‘Sweet Round’. Pepino fruit contains slightly higher amounts of fructose than glucose, and contents of both sugars do not change dramatically during ripening. However, there is a sharp increase in sucrose as ripening progresses. Sucrose content in green fruits is very low or not detectable, while it is the predominant sugar when ripe, accounting for about 50% of the total sugars. The ripening process is characterised by a decline in insoluble fibre accompanied by an increase in total sugars and accumulation of sucrose. The important interaction clone × growing cycle indicates that selection for high sugar content should be carried out independently for each growing cycle. © 2000 Society of Chemical Industry

Characterization of Spanish Tomatoes using Aroma Composition and Discriminant Analysis

Nowadays, tomato breeders are trying to associate high fruit firmness, long shelf life, high disease resistance, and good flavor; however, breeding for sensory quality has been severely restricted up to date. In this study, a system specifically designed for the analysis of low amounts of material has been set up and tested to quantify the volatile aroma constituents of tomatoes. Ten volatile compounds with a major contribution to tomato aroma have been quantitatively determined in two traditional tomato types (Muchamiel and De la Pera) and one hybrid type (Odissea). Both traditional types presented higher intensities of tomato odor and aroma according to a trained panel and they were more accepted by a consumer panel than the hybrid tomatoes. The traditional tomatoes showed significantly higher contents of most of the volatiles studied. Significant differences among traditional and hybrid types were found and a mathematical model that successfully discriminated among tomato types was developed using only the concentrations of six volatile compounds: 3-methylbutanal, 1-penten-3-one, hexanal, trans-2-hexenal, 1-hexanol, and 2-isobutylthiazole. This mathematical model could help in using volatile determination as a possible tool in tomato breeding programs and in maintaining and improving traditional Spanish tomato cultivars.

Comparative post-harvest behaviour of traditional and virus-resistant Muchamiel tomatoes.

BACKGROUND Nowadays, organoleptic quality is the primary objective for almost all tomato breeding programmes. In this study, post-harvest behaviour of a breeding line with genetic resistance to important viruses (tomato mosaic virus, tomato spotted wilt virus and tomato yellow leaf curl virus) has been compared with the original traditional landrace (Muchamiel). The breeding line has been obtained by backcrossing, introgressing three resistance genes but aiming to keep the quality characteristics of the traditional variety. Tomatoes were picked at random and stored at 10 degrees C for 13 days. Quality analyses were made in both tomato samples: weight loss, colour, respiration rate, ethylene production, maturity index, instrumental hardness and sensory evaluation with trained panel. RESULTS Fruits of the breeding line were characterized by higher hardness even with a higher maturity index. Results of sensory tests were in agreement with instrumental measurements. Organoleptic quality of Muchamiel virus-resistant tomatoes was at least as high as that of traditional tomatoes, reaching the best scores in odour and aroma at the 13th storage day. CONCLUSION Although a long time has been required to develop the breeding line, results indicate that organoleptic fruit quality has been recovered through backcrossing, confirming the success of the breeding programme.

Identification, introgression, and validation of fruit volatile QTLs from a red-fruited wild tomato species.

Highlight Over 100 fruit volatile QTLs were identified in a RIL population derived from the red-fruited wild species Solanum pimpinellifolium and a fresh market tomato variety ‘Moneymaker’ and subsequently confirmed in introgression lines.

Effect of Recent Genetic Improvement on Some Analytical Parameters of Tomato Fruit Quality

Abstract Poor flavor in tomato fruit is a serious consumer concern. It could be said that tomato flavor has declined as variety selection and tomato production has placed emphasis on yield, fruit size, firmness, disease resistance, and processing performance and not on aspects of organoleptic fruit quality. Consumers frequently associate recent varieties with a lack of flavor, although such an association has not been proven. We have reviewed the scarce available literature on the influence of recent genetic improvement on quality attributes of tomato. As a case study, we have analyzed several parameters related to fruit quality in some traditional Spanish cultivars and commercial F1 hybrids of tomato. Organic acids and sugars were determined by high performance liquid chromatography (HPLC). Sodium (Na), potassium (P), and phosphorus (K) were analyzed by atomic absorption spectroscopy. Levels of respiration and ethylene production were measured, and fruit firmness was determined using a texture analyzer. All determinations were performed at two maturity stages, representing two frequent consumption stages. Differences between traditional cultivars and hybrids were found for respiration rates, ethylene production, P and K fruit contents. We also found important differences between “old” and “modern” cultivars for their organic acids profile. All cultivars showed similar levels of malic and succinic acids, but the modern hybrids showed a ∼75% higher content of citric acid. This could be due to the F1 hybrids carrying chromosomal segments recently introgressed from wild Lycopersicon species. The influence of recent genetic improvement on quality attributes of tomato fruit is discussed.

Benomyl sensitivity assays and species-specific PCR reactions highlight association of two Colletotrichum gloeosporioides types and C. acutatum with rumple disease on Primofiori lemons

Rumple is a serious peel collapse of Primofiori lemons in the southeast of Spain with an unresolved aetiology. Symptoms typically occur on fruits at ripening under wet conditions as dark sunken lesions producing premature fruit drop and damaged fruits unacceptable for fresh commercialization. A total of 16 Colletotrichum spp. isolates established from rumple-affected lemons collected during the autumn of 2007 from two different orchards were characterized by molecular and phenotypic assays and compared with reference isolates. Species-specific PCR reactions using β-tubulin 2 nucleotide sequences showed Colletotrichum gloeosporioides to predominate (81.5%) with limited occurrence of C. acutatum (18.75%). Among the C. gloeosporioides isolates, five (38.5%) showed benomyl resistance and eight (61.5%) were highly sensitive to the fungicide. The limited occurrence of C. acutatum could be related to factors such as the presence of both species on the same fruit, unfavourable meteorological conditions and low disease incidence. This work reveals an association of C. gloeosporioides and C. acutatum isolates with rumple disease of lemons and expands the range of C. acutatum on citrus.

Quality assessment of tomato landraces and virus‐resistant breeding lines: quick estimation by near infrared reflectance spectroscopy

BACKGROUND Several tomato landraces are very popular in south-eastern Spain for their organoleptic fruit quality, but these cultivars are highly susceptible to several viruses. A breeding programme is being carried out for the introduction of virus resistances into these landraces. In the last steps of our breeding programme a high number of breeding lines must be evaluated for agronomic and organoleptic quality parameters. Near infrared reflectance spectroscopy (NIRS) technology shows considerable promise and is ideally suited to the requirements of breeders. RESULTS Significant differences between a set of 35 tomato breeding lines, seven landraces and one commercial hybrid were observed for quality and mineral content parameters, suggesting that there are considerable levels of genetic diversity between the cultivar groups studied. Using NIRS on dry samples of tomato constitutes a feasible technique to estimate the content of several minerals (C, N, P, K, Ca, Na, Mn, Mg and Cu) according to the coefficient of determination for calibration (R(2) > 0.90). NIRS estimations of soluble solids content and titratable acidity obtained were considered useful only for general screening purposes. CONCLUSIONS NIRS technology may be a useful tool in the selection of lines coming out of tomato breeding programs, allowing a quick estimation of mineral content. However, the estimation of soluble solids content and titratable acidity by NIRS must be improved.