Fusarium wilt of watermelon can be effectively managed by grafting with resistant rootstocks. Excision and regeneration of grafted seedling roots is a common practice among cucurbit-grafting nurseries that has not been thoroughly examined. The objectives of this study were to compare the performance of grafted and nongrafted watermelon plants under both greenhouse and field conditions when inoculated with Fusarium oxysporum f. sp. niveum (FON) race 2, and assess the effect of root excision on growth of grafted plants with Cucurbita moschata and Cucurbita maxima × C. moschata rootstocks. Two greenhouse experiments (Fall 2015 and Spring 2016) and one field trial (Spring 2016) of seedless watermelon ‘Melody’ were conducted in this study. In both greenhouse experiments, inoculated, nongrafted watermelon plants showed a significantly higher percentage of recovered Fusarium spp. colonies (70% to 75%) compared with grafted treatments (0% to 7.5%). Some plant growth measurements, including the longest vine length and aboveground fresh and dry weight, indicated less vigorous growth for nongrafted plants compared with the grafted treatments. Significantly higher percent recovery of Fusarium spp. below the graft union was observed in the grafted plants with root excision and regeneration treatment (3.7%) in contrast to the intact root treatment (0.5%), suggesting that the root excision method may possibly create entry points for FON infections. Overall, the root excision treatment showed little influence on aboveground growth and root characteristics of grafted plants. Yield of grafted watermelon with FON inoculation in the fumigated field trial was significantly higher than that of noninoculated, nongrafted ‘Melody’ (NGM) control as reflected by the increase of fruit number and size. Averaged over all the grafted treatments, the increase in marketable fruit number and weight reached 108.3% and 240.9%, respectively, and the total fruit number and weight increase was at 80.0% and 237.2%, respectively. However, grafted plants also exhibited greater levels of root-knot nematode infestation as indicated by the significantly higher root galling ratings. Results from this study demonstrated that grafting with squash rootstocks can effectively limit FON colonization in seedless watermelon plants, although more research in rootstock selection and testing is needed to optimize the use of grafted plants for improving plant growth and fruit yield.

Strains of Rhizobium CR 113; CR 477; CF-1 (equal to CIAT 151); 6bIII; 2bIII and HbI, along with noninoculated and non-nitrogenated treatments – 30 kg/ha N without inoculation and high N, 150 kg/ha N – in three environments in the Pinar del Rio, Matanzas and Holguin provinces were validated in three types of soil: ferrous quartzitic, ferrous red, and non- carbonated brown with a low total nitrogen content (less than 65kg/ha N). The BAT 58 bean variety was used. Production of aerial and nodular dry matter during the development phase (R6), production of aerial dry matter and total nitrogen consumption in the (R8) phase, and bean production in the (R9) phase, were quantified. Results showed a lower significant difference in the treatments without inoculation, as compared to the treatments with high nitrogen content and 30kg/ha N plus seed inoculation. No difference was found between the treatment with high N applications, and the ones inoculated with Rhizobium strains plus 30 kg/ha.

The capacity of five common bean genotypes from the germ plasm bank at CIAT, Colombia (Río Tibaji, APN 18, Carioca, G 14665, and G19441) to fix nitrogen from the atmosphere was evaluated. An experiment was carried out with plants grown in 16-liter capacity plastic boxes with a highly aerated and nitrogen-free nutrient solution (400 ml of air/solution liter/min). In the first box the CIAT 899 Rhizobium strain was innoculated, and in another box the CR 477 strain from Costa Rica, both from CIAT; a third box was reserved for CF1 of national origino The experimental design consisted of random blocks with four repetitions. In order to determine the dry mass of the aereal part (DMAP), the radicular dry mass (RDM), and the nodular dry mass (NDM), the plants were cut in the R7 developmental phase. With respect to NDM, the carioca genotype and the CF1 strains were statistically superior to the rest (P<0,00l); however, the major nitrogen fixers were the G 14665 genotype - the best combination between NDM and fixation efficiency - and the CIAT 899 strain, which was 2.4 times more efficient (N mgl NDM g) than the rest. This shows that the NDM production is not a determining variable when genotypes or strains with a high capacity for nitrogen fixation in the atmosphere are being selected.