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María Victoria Huitrón-Ramírez, Marcia Ricárdez-Salinas, and Francisco Camacho-Ferre

One of the major problems of watermelon production is the decrease of fruit yield and quality caused by soil diseases. Soil disinfection with methyl bromide (MB) has been used to prevent fungus attacks; however, its use is being restricted because this substance damages the ozone layer. Searching for new MB alternatives, field experiments were carried out in open field in soils infested with Olpidium bornovanus and melon necrotic spot virus in Colima, Mexico, where watermelons had only been grown previously using soil fumigation with MB. Yield and quality of watermelon cultivar triploid Tri-X 313 grafted on two rootstocks of Cucurbita maxima × Cucurbita moschata (‘RS841’ and ‘Shintosa Camelforce’) were evaluated during 2 consecutive years. Each experiment had five treatments, two of them with nongrafted plants at a density of 3472 plants/ha with and without MB fumigation. The remaining three treatments had grafted plants in nonfumigated soil with plant densities of 2778, 2083, and 1740 plants/ha. The use of watermelon grafted on ‘RS841’ and ‘Shintosa Camelforce’ rootstocks significantly increased the average fruit weight and the total yield of watermelon in soil without the need for MB. Grafting may be considered as an alternative MB fumigation. With the use of grafted watermelon plants, planting density may be reduced by 50%, obtaining higher yields than those obtained from nongrafted plants grown on fumigated soil except for ‘Tri-X 313’ grafted on ‘Shintosa Camelforce’ in 2006–2007. Fruits harvested from grafted plants had higher firmness than those harvested from nongrafted plants without affecting the content of soluble solids.

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Rafael Fernández-Muñoz, María Salinas, Marta Álvarez, and Jesús Cuartero

Genetics of resistance to Tetranychus urticae Koch and of glandular trichomes of Lycopersicon pimpinellifolium accession TO-937 in a cross between susceptible L. esculentum Mill. `Moneymaker' and resistant TO-937 was studied in a greenhouse experiment. Parents, F1, F2, and two BC1 generations, interspersed with susceptible tomato plants to avoid negative interplot interference, were artificially infested. Mite susceptibility was evaluated by a rating based on plant capacity to support mite reproduction. TO-937, BC1 to TO-937, and F1 were resistant, `Moneymaker' susceptible, and the F2 and the BC1 to `Moneymaker' segregated. Resistance was controlled by a single dominant major locus, but modulated by unknown minor loci. TO-937 presented type IV glandular trichomes, their presence governed by two dominant unlinked loci. Type IV trichome density correlated to resistance; however, a causal relationship between type IV trichomes and mite resistance could not be definitively established. The relatively simple inheritance mode will favor successful introgression of resistance into commercial tomatoes from the close relative L. pimpinellifolium.

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Silvia Jiménez, Mónica Pérez, Blanca María Plaza, Roberto Salinas, and María Teresa Lao

The study of models for better nutrient uptake estimation can help to improve integrated fertigation management, allowing enhanced water and fertilization use efficiency. The aim of this work was the development of empirical models that permit the prediction of the phosphorus (P) nutritional needs of Dieffenbachia amoena to increase P use efficiency in a recycled system. To achieve this, P uptake was correlated to climate parameters, such as temperature (T), vapor pressure deficit, and global radiation (Rg), and to growth parameters such as leaf area index (LAI). In addition, the influence of the N form supply (NO3 -N or NH4 +-N) on P uptake was studied. The trial was carried out with Dieffenbachia amoena ‘Tropic Snow’ plants growing in a recycled system with expanded clay as substrate. The crop was placed in an INSOLE buried solar greenhouse, with the plants supplied with equal amounts of N, differing in the percentage of the N form applied: Ta (100 NO3 : 0 NH4 +), Tb (50 NO3 : 50 NH4 +) and Tc (0 NO3 : 100 NH4 +). The N form applied to Dieffenbachia amoena ‘Tropic Snow’ plants affects P and N uptake, but it does not influence K uptake. Nitrogen and P uptake rates are higher in the plants supplied with NH4 + or NO3 + NH4 + than in the plants provided with NO3 alone. The supply of a combination 50 NO3 : 50 NH4 + improves P use efficiency. The study also indicates the possibility of predicting the P uptake rate and P uptake concentration using the proposed models. Phosphorus uptake can be estimated with a model dependent on the LAI in the NO3 -N treatments and on the LAI and Rg in the NH4 +-N treatments. The P uptake concentration can be calculated with the P uptake, estimated through the previous model, and the experimental water uptake. This parameter would permit the nutritive solutions design, decreasing nutrient losses in open systems.