CHARACTERIZATION OF NOVEL TOMATO FRUIT FIRMNESS TRAIT THAT CONSERVES FLAVOR AND NUTRITIONAL QUALITY
Development of tomatoes that are flavorful and nutritious yet firm with long shelf life is the holy grail in tomato improvement. So far, tomato genes that inhibit ripening have been successfully used to improve firmness and shelf life. Unfortunately, this approach has negatively affected flavor, and nutritional value. As a result, it is generally accepted that most modern tomato cultivars have lost their flavor reducing consumption and supermarket sales. The vegetable breeding program at Weslaco identified a new trait for fruit firmness in tomato conserves good flavor and quality since the ripening process is not inhibited. Impact: TAM-SP18-157 reaches an average compression peak of 1.571 kilograms force (KgF), with fruits 70% more firm as compared to the average firmness in the population (0.92 KgF). TAMU trait that can be used to substantially improve fruit flavor and shelf-life characteristics, meeting both consumers’ and retailers’ demands on fruit quality.
Figure 1. Tomato breeding line TAM-SP18-157 having novel firmness trait
DEVELOPMENT OF TOMATO YELLOW LEAF CURL VIRUS RESISTANT CULTIVARS
The main disease affecting tomato production in South Texas is the tomato yellow leaf curl virus (TYLCV), which is vectored by whiteflies. Several major resistance genes for TYLCV have been identified, but they need to be introgressed and stacked into locally adapted cultivars to ensure long-lasting disease resistance. Current efforts of the breeding program are focused to introgress resistance genes into heat-tolerant breeding lines. Marker-assisted selection is being used to increase selection efficiency by allowing us to only evaluate plants carrying the resistance gene(s) in the field.
Figure 2. Breeding for TYLCV resistance.
A) TYLCV symptoms, B) marker-assisted selection, C) Field evaluation
DEVELOPMENT OF MOLECULAR TOOLS FOR DISEASE RESISTANCE SELECTION IN SPINACH
Breeding for spinach improvement requires new methods to speed up the development of cultivars with increased yield potential and disease and pest resistance. In Texas, the most yield-limiting diseases in spinach production include White Rust (WR) and recently Anthracnose, caused by Albugo occidentalis and Colletotrichum dematium, respectively. Since natural infection levels in the field varies year-to-year, conventional selection of resistant cultivars in the field is time consuming and unreliable. Therefore, in order to improve cultivar-development efficiency, the breeding program is evaluating spinach-breeding lines for disease resistance to develop molecular markers linked to resistance traits.
Figure 3. White rust symptoms in spinach
IDENTIFICATION AND INTROGRESSION OF RESISTANCE AGAINST THE POTATO PSYLLID IN TOMATO
To date, no commercial tomato cultivar carries resistance to the potato psyllid (PP), the vector of “Candidatus Liberibacter solanacearum” (Lso) and the causal agent of tomato vein greening in tomato and other economically important diseases in solanaceous crops. As a result, farmers rely solely on chemical applications to control the insect. It is imperative to develop resistant cultivars in combination with management strategies to reduce yield losses. As a first step to develop resistant cultivars, the breeding program is screening wild tomato relative species to use as a resistance source. Identified resistant wild tomatoes are being crossed with advanced tomato breeding lines to develop resistant cultivars.
Figure 4. Potato psyllid resistance screening using no-choice test
IDENTIFICATION AND CHARACTERIZATION OF PLANT DEFENSIVE OXYLIPINS INVOLVED IN RESISTANCE TO THE POTATO PSYLLID AND ITS TRANSMITTED BACTERIA
Oxylipins represent a large, diverse group of fatty acid-derived compounds primarily generated through enzymatic oxidation of linoleum and linolenic acid. Synthesis of plant oxylipins is regulated in response to plant stress, and resulting oxylipins participate in signaling and defense. The goal of this project is to identify oxylipins that contribute to plant defensive signaling and their regulatory network in response to PP-Lso infection as a first step to develop tomato and potato selection targets to enhance plant resistance. Antibiotic and insecticide properties of phloem mobile oxylipins against the PP-Lso are being evaluated when applied directly to leaves or to artificial diets. Parameters tested include insect survival/fecundity and bacterial load change in both insect an plant.
Figure 5. Evaluation of antibiotic and insecticide properties of oxylipins using artificial diets
EVALUATION OF TOMATO PRODUCTION UNDER PROTECTED STRUCTURES
Protected structures such as high tunnels, enthuses, and greenhouses provide an alternative to tomato production in harsh environmental conditions by extending the growing season. The breeding program is currently leading a project to evaluate the agronomic and economic feasibility of covered structures as an alternative to open field production to reduce yield loses caused by insect-transmitted diseases and to extend tomato growing season. The project aims to develop an extended information network to provide grower education on factors influencing profitable production practices specifically developed for locally and regionally produced fresh market tomatoes.
Figure 6. Nethouse production in South Texas