b'and seasons), this necessitates, for every type, specific genetics and screening conditions. Therefore, the investment needed to breed for one type, or another greatly differs. Yield of any crop matters, but Zonneveld 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 disorders like tipburn and a high percentage of harvestable plants per ha. For segments where yield is important, we are measuring yield in our trials. Schut 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.Prakash explains that whilst yield is important in all let-tuce market segments, its especially important in those seg-ments where the crop is cultivated in poor growing conditions, such as winter. The yield is less related to region but very much influenced by maturity stage, season slot, soil type and growing conditions. In the early stages of variety development, we gen-erally measure the size of the heads at their harvesting maturity stage, he says. Later, when varieties make it to the precommer-cial 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, says Zaccaria. She adds that the main differences in varieties of their babyleaf lettuce is whether its grown in the field or greenhouse. With the latter, the varieties grow more quickly, and the leavesDifferent types of lettuce in the field. Source: Syngentaare more tender, so, in our breeding program, she says, we focus a lot on leaf texture. ANOTHER BREEDING TARGET:FRESH CUT DISCOLOURATIONSusceptibility 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 directly related to this condition and Meridiem is working with very promising results on varieties that incorporates resistance to this bacterium.Visser notes that there is a lot of research being conducted to find the molecular keys to reduce oxidation of the polyphe-nol-rich cells that are damaged or stressed around the cut surface. On this note, Schut reports that a few years ago, Rijk Zwaan has introduced a new trait, the so-called Knox trait, which causes a delay in wound induced oxidation. This trait is the result of a non-expressed gene in the phenyl-propanoid pathway, he says, and it was first found in a butterhead lettuce plant 15 years ago.Visser adds that the use of different post-harvest handling methodsreducing the temperature during processing and stor-age, for example, and the use of modified atmosphere packaging (MAP)can make a big difference in reducing browning. The final solution for the marketplace would be a combination of MAP and genetics, he says. The latter providing most benefit once the product reaches the consumer and the packaging is openedLettuce Breeding Managers Johan Schut and Jair Haanstra. Source: Rijk Zwaanfor the lettuce to be eaten over several days. EUROPEAN-SEED.COMIEUROPEAN SEED I 7'