b'celeriac, BASF Vegetable Seeds, explains that because its affected by many factors (cultural preferences, uses, require-ments for different production systems, climates and seasons). This necessitates, for every type, specific genetics and screening conditions, Visser says. Therefore, the investment needed to breed for one type, or another greatly differs.Yield of any crop matters, but Olaf Zonneveld, Global R&D Crop Lead Salads of Syngenta Seeds, is of the view that yield in ton/ha is less important for lettuce than in other crops. A large part of the lettuce is sold by piece and not by weight, he says. For the fresh market, yield exists mainly in quality traits like no visible diseases on the head, no internal dis-orders like tipburn and a high percentage of harvestable plants per ha. For segments where yield is important, we are measuring yield in our trials. Johan Schut, lettuce breeding manager of Rijk Zwaan, notes that in general, lettuce yield has increased over time due to a reduced impact of factors that lead to a bad harvest, such as susceptibility to abiotic stresses, diseases and pests. Gowtham Prakash, Pre-Breeder leafies at BASF Vegetable Seeds, explains that whilst yield is important in all lettuce market segments, its especially important in those segments where the crop is cultivated in poor growing conditions, such as winter. The yield is less related to region but very much influenced by matu- Lisa Zaccaria. rity stage, season slot, soil type and growing conditions. In the early stages of variety development, we generally measure the size of the heads at their harvesting maturity stage, he says. Later, when varieties make it to the precommercial stage, we collect data on yield per plant and square meter, depending on the type of product: whole head-hand harvest or leaves-mechanical harvest. Yield of Maraldis babyleaf lettuce is evaluated by both leaf count and leaf weight at maturity. Also, the suitability of our varieties for multiple cuts increases their profitability, Lisa Zaccaria, lettuce breeder at Maraldi. She adds that the main differences in varieties of their babyleaf let-tuce is whether its grown in the field or greenhouse. With the latter, the varieties grow more quickly, and the leaves are more tender, so, in our breeding program, she says, we focus a lot on leaf texture.Another Breeding Target: Fresh Cut DiscolorationSusceptibility to browning or pinking at the cut surfaces is a factor that affects purchase choice at the grocery store and one with which restaurants also have to contend. Browning or pink-ing after lettuce is cut is related to the oxidation of leaf tissue. Most pinking problems start before harvesting and extend to bagging for fresh produce or cutting for processing, Garca explains. The bacteria Pseudomonas marginalis is directlyLettuce Breeding Managers Johan Schut and Jair Haanstra out in related to this condition and Meridiem is working with verythe field.FEBRUARY 2021SEEDWORLD.COM /57'