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Plant diseases are among the major causes of crop yield losses around the world. To confer disease resistance, conventional breeding relies on the deployment of single resistance (R) genes. However, this strategy has been easily overcome by constantly evolving pathogens. Disabling susceptibility (S) genes is a promising alternative to R genes in breeding programs, as it usually offers durable and broad-spectrum disease resistance. In Arabidopsis, the S gene DMR6 (AtDMR6) encodes an enzyme identified as a susceptibility factor to bacterial and oomycete pathogens. Here, we present a model-to-crop translational work in which we characterize two AtDMR6 orthologs in tomato, SlDMR6-1 and SlDMR6-2. We show that SlDMR6-1, but not SlDMR6-2, is up-regulated by pathogen infection. In agreement, Sldmr6-1 mutants display enhanced resistance against different classes of pathogens, such as bacteria, oomycete, and fungi. Notably, disease resistance correlates with increased salicylic acid (SA) levels and transcriptional activation of immune responses. Furthermore, we demonstrate that SlDMR6-1 and SlDMR6-2 display SA-5 hydroxylase activity, thus contributing to the elucidation of the enzymatic function of DMR6. We then propose that SlDMR6 duplication in tomato resulted in subsequent subfunctionalization, in which SlDMR6-2 specialized in balancing SA levels in flowers/fruits, while SlDMR6-1 conserved the ability to fine-tune SA levels during pathogen infection of the plant vegetative tissues. Overall, this work not only corroborates a mechanism underlying SA homeostasis in plants, but also presents a promising strategy for engineering broad-spectrum and durable disease resistance in crops.

The Mi gene in tomato confers resistance to Meloidogyne javanica, M. incognita, and M. arenaria, the most common tropical root-knot nematode (RKN) species found in Florida. Fusarium wilt (Fol) is another major problem in Florida tomatoes which may interact with RKN and cause more plant damage. To study the interactions between RKN, Fusarium, and Mi in tomato, two greenhouse experiments were conducted. Both experiments used different isolines (with and without I-3 and Mi genes) of the tomato cultivar Tasti Lee®. In the first experiment, all four isolines were subjected to two levels of RKN (~10,000 eggs/pot and no eggs) and two levels of Fol (1000 cc soil with 1,000 cfu/g at planting and no Fol), both applied at planting. In the second experiment, the two isolines without I-3 were exposed to the same two levels of RKN as described above and three levels of Fol (50 ml Fol with 1×106 cfu/m at planting, at 10 DAT, and no Fol). Fol reduced root-knot infection and reproduction when both Fol and RKN were inoculated at planting but not when Fol was inoculated 10 days later. Plant damage from Fol was exacerbated in the presence of RKN, especially when both pathogens were present at planting. Isolines with I-3 grew better in Fol-inoculated soil but had no effect when Fol and RKN were both present. Isolines with Mi gene reduced RKN infection and reproduction but did not affect plant damage caused by Fol. In summary, while RKN reproduction was reduced in the presence of Fol, the overall plant damage was more severe when both pathogens were present.

Psychophysics was utilized to understand how the metabolite profile of tomato juice influenced consumer response between pasteurization methods. Overall liking, tomato flavor liking, flavor intensity, and sweetness intensity were dependent on specific volatile compounds. Overall liking was most influenced by tomato flavor, which correlated with flavor intensity. Tomato juice flavor can be delineated by volatiles impacting consumer perception, thirty‐nine of which significantly correlated with sensory attributes. Three volatiles may enhance sweetness intensity, suggesting that the presence of these volatiles can enhance consumer preference. Thermal treatments modified the volatile profile of tomato derivatives due to Maillard reaction activation, carotenoid co‐oxidation, and fatty acid oxidation. Enhanced thermal processing promoted the formation of cooked note volatiles and loss of green note volatiles. Principal component analysis revealed commercially processed tomato juice to be separated from the pilot juices due to cooked note volatiles. Desirable levels of cooked note volatiles may depend on the target market. Novelty impact statement: Sensory analysis showed that panelists are willing to purchase a novel processed tomato juice made from Florida fresh market cultivars. With sensory and chemical analysis, individual volatiles present in the juice correlated with increased overall liking and flavor/sweetness intensity. Metabolite markers can be used to help improve tomato juice flavor. [ABSTRACT FROM AUTHOR]

Florida tomatoes are primarily produced for the fresh market and have not been widely used in processed tomato products. This study tested six Florida fresh market tomato cultivars (FLA 8083, FLA 8297, FLA 8344, FLA 8570, FLA 8924 and Garden Gem) to determine suitability for juice production. Genetic and environmental‐induced variation was studied, and analyses identified metabolites that influenced the perceptual and hedonic responses of tomato juice. Each cultivar was processed into juice by hot breaking at 86 ˚C for 3.5 minutes and then pasteurization at 121 ˚C for 42 seconds for a shelf stable product. Among the six pilot products, FLA 8344 cultivar had significantly higher soluble solids content and titratable acidity in all three experiments. The pH of each of the tomato juices made from fresh market tomatoes was within or below the typical range for tomato juice. Garden Gem was consistently rated significantly (P ≤.05) higher for aroma, overall liking, tomato flavour, texture and overall flavour. In all three experiments, tomato juice from a fresh market cultivar simultaneously had the greatest abundance of green‐note volatiles (hexanal, 1‐hexanol, (Z)‐3‐hexen‐1‐ol, etc) and the lowest abundance of cooked‐note volatiles (dimethyl sulphide, methional and furfural). Consumer acceptance increased as salt concentration increased and while season had minor effects on the chemical composition of the juice, consumers preferred the Spring processed tomato juice over Fall. [ABSTRACT FROM AUTHOR]

Bemisia tabaci MEAM1 (Gennadius), the sweetpotato whitefly, transmits Tomato yellow leaf curl virus (TYLCV), which causes significant yield losses annually in Florida and other tomato-producing regions. Field trials were carried out at the University of Florida's Gulf Coast Research and Education Center to evaluate integration of plastic mulch type, at-plant insecticide, and tomato variety for management of the sweetpotato whitefly and TYLCV. The tomato varieties Charger, Rally, and Tygress had significantly lower season-long densities of whitefly eggs and nymphs than Florida-47 in one or more trials. Aggressive chemical control measures failed to reduce virus incidence in two of the three trials and did not improve yield. In 2013, when virus pressure was extremely high, yield in the susceptible variety was decimated, but virus-tolerant varieties produced a crop. Egg and nymph densities tended to be lowest on TYLCV-tolerant varieties and on tomato grown on metalized mulch. Differences in yield were primarily due to tomato variety and TYLCV incidence. Intensive insecticide use common in Florida tomato production may reduce losses when viral pressure is moderate, but not when migration of viruliferous whiteflies into the field is constant. Without significant winter freezes or a coordinated host-free period to reduce whitefly populations, insecticidal control and repellent-metalized mulches will offer limited protection compared with genetic tolerance to the virus, which may also be overcome under high virus pressure. [ABSTRACT FROM AUTHOR]