Identification of an allele attributable to formation of cucumber-like flavor in wild tomato species (Solanum pennellii) that was inactivated during domestication

Carbon 6 (C6)-aldehydes formed by fatty acid 13-hydroperoxide lyase (13HPL) specific to fatty acid 13-hydroperoxides (13-HPO) are important flavor constituents in fresh tomato fruits. C9-aldehydes are usually formed by 9/13HPL showing dual specificity to 9- and 13-HPOs and are scarcely found in tomato fruits. Mature red fruits of one of the introgression lines, IL1-4, generated by hybridization of a cultivated tomato (Solanum lycopersicon) to its wild relative Solanum pennellii, form high amounts of C9-aldehydes upon homogenization. The IL1-4 fruits showed high 9/13HPL activity. One of the genes isolated from IL1-4 showed a high similarity to plant 9/13HPLs. Recombinant proteins expressed in Escherichia coli showed 9/13HPL activity. Cleaved amplified polymorphic sequence analyses indicated that the gene was specific to IL1-4 and S. pennellii. S. lycopersicon had a gene having high similarity to the S. pennellii gene. It was absent in IL1-4. Among the differences of amino acid residues found between the two genes, a Cys to Ser exchange may be responsible for the inactivation of resultant protein product of S. lycopersicon gene because the Cys is an essential amino acid residue for HPL activity. From these observations, it could be assumed that a tomato gene corresponding to S. pennellii 9/13HPL gene had been inactivated through domestication of tomatoes.     

The potential of ripening mutants for extending the storage life of the tomato fruit

Summary The effect of the fruit ripening mutants rin, gr, nor and Nr on storage life and pigmentation was investigated in homozygous material, in heterozygous F₁ combinations between the mutants with the colour mutant hp and with the normal cv. Kewalo. Crosses with nor showed a 3-to 5-fold increase in storage life in comparison with the normal cv. or with hp. Maximum pigmentation of the fruits of crosses with nor was pale-red with vineripened fruit and pink with fruit harvested at the breaker stage and ripened on the shelf. The ripening inhibitory effect of rin in the different F₁ combinations was less pronounced than that of nor, and the colour of the fruits was improved. Fruits of the F₁ cross between rin and nor showed greatly improved storage life and developed pink or pale red colour. Most heterozygotes with hp showed improved pigmentation. Problems anticipated in utilizing ripening mutants in breeding for improved keeping quality are discussed.     

Differential effects of tomato (Lycopersicon esculentum mill) matrix on the volatility of important aroma compounds

Significant tomato matrix effects on the volatility of certain fresh tomato odorants were found. The concentrations of odorants such as (E,E)-2,4-decadienal, beta-damascenone, and beta-ionone, in crushed fresh tomato fruit obtained by solid-phase microextraction (SPME), resulting from a tomato matrix calibration curve were 5.5-, 2-, and 12-fold higher, respectively, than those calculated by calibration based on buffer solutions. Static headspace analyses indicated that, in most cases, the tomato matrix significantly retains the odorants relative to the buffer solution. Thus, the concentration of odorants in the headspace of tomato is lower than expected compared to a simple matrix such as buffer. CaCl(2), although needed in crushed fruit tissue to block enzymatic activity, was found to interact specifically with 2-isobutylthiazole, reducing its content in the headspace by at least 6-fold. If a matrix effect is found, analysis of the odorant molecule contents in the headspace rather than in the food is recommended in order to better evaluate their access to the olfactory receptors.     

Fruit set and yield of Pepino Dulce response to nitrate‐nitrogen and salinity levels and thinning of side branches and trusses 1

Three pepino dulce (Solanum muricatum Ait.) selections were fertigated with nitrate‐nitrogen at 3, 6, or 12 mmol/L, and 0,3, or 6 dS/m chloride ions. Plants treated with nitrate‐nitrogen at 6 mmol/L bore heavier yields of larger fruit than those at 3 mmol/L. Further increase in nitrate‐nitrogen application to 12 mmol/L did not result in yield increase. Salt decreased yield in all cases. Heavy fruit set was recorded in plants trimmed to two main shoots, and thinning to three sets per truss resulted in even fruit distribution between trusses.     

Greenhouse technique to evaluate onion resistance to pink root

Summary An assay for resistance of onion to pink root Pyrenochaeta terrestris was developed, employing infested vermiculite medium with an adequate inoculum concentration of the fungus to minimize escapes of susceptible plants.Plant material other than seed was used. Either root-excised 6–8 week-old seedlings or onion sets were planted in infested vermiculite, and kept for two successive 2-week periods of growth differing in light and temperature regimes. During the first phase a short-day regime of 10 h and 17±1°C was kept, under which a vigorous root system was obtained. For an additional 12–14 days under 26±1°C and 12 h light the prolific roots were then exposed to the optimal temperature for disease development.This technique enables one to distinguish easily between susceptible Allium cepa material and a resistant line of A. fistulosum.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1022-E, 1984 series.