California processing tomatoes: Morphological, physiological and phenological traits associated with crop improvement during the last 80 years

• We evaluated a total of 8 cultivars released since 1930s until 2000s.
• A total of 95 variables were evaluated using multivariate statistics.
• No single trait seems to have driven yield increases in processing tomato cultivars.
• Distinct assembly of traits for many of these top yielding cultivars is presented.
• Trait associations relevant to crop improvement are discussed.

Breeding has greatly increased yields of many crops, but the contributions of particular morphological, phenological and physiological traits to these higher yields are rarely well understood. In the past 50 years, California processing tomato yields per hectare have more than doubled. This study evaluated a group of important processing tomato cultivars released over the past 80 years in California. The objective was to assess how a suite of traits might be associated with genetic improvement for yield gains. A wide array of morphological, physiological and phenological traits and relevant environmental variables was evaluated in the field for a discrete set of eight cultivars originating from a common ancestor. Multivariate statistics were used to analyze the set of 95 variables to understand how cultivars became adapted to a more mechanized agronomic management while also producing higher yields. No single trait seems to have driven yield increases. Instead, distinct assemblies of traits characterize the processing tomato cultivars in different eras. For instance, certain phenological traits (early flowering and concentrated fruit set) were associated with a set of morphological traits (smaller canopies and low vegetative biomass), along with gains in physiological traits (biomass N concentration and photosynthetic rates) in modern varieties. These results provide a platform to examine new suites of traits that could be relevant for future breeding and crop improvement.