Plant breeding for organic and sustainable, low-input agriculture

Cultivar x growing cycle interaction in lettuce grown under certified organic conditions:
implications for selection, breeding and use of diversity
María Dolores Raigón 1 , Jaime Prohens 2 , Fernando Nuez 2
1 Departamento de Química, Universidad Politécnica de Valencia, Spain
2 Instituto de Conservación y Mejora de la Agrodiversidad Valenciana, Universidad Politécnica
de Valencia, Spain
The increased demand of organically produced lettuce (Lactuca sativa) has led to the necessity to
offer an extended period of supply of the produce. While this can be achieved by growing the
crop in different regions or by the use of protected cultivation, the use of several growing cycles
in a certain region, combined with appropriate varieties can contribute to extending the period of
production, which is important if the combination of “organic + local” production is pursued.
Given that the conditions in early and late cycles may be different from those of the common
cycle, interactions cultivar x growing cycle may exist.
Fifteen varieties of lettuce from six varietal groups (“Batavia”, “butterhead”, “lollo green”, “lollo
red”, “oakleaf green”, and “oakleaf red”) were grown in three growing cycles (early,
intermediate, and late) under organic cultivation conditions in a farm of the Committee of
Organic Agriculture of the Valentian Community situated in Sagunto (Valencia, Spain). The
transplants of the early, intermediate and late cycles were made in December, January and
February, respectively, using a completely randomized design, with 3 replications and 32 plants
per replication. Traits evaluated have been total and commercial yield, gross and net weight, size
of the head, and resistance to bolting.
Under the organic cultivation conditions tested, there are important effects of cultivation cycle,
varietal group, cultivar within varietal group, as well as interactions between cultivation cycle
and varietal group, and between cultivation cycle and cultivar within varietal group. In general,
the best average results are obtained in the intermediate cycle, followed by the late cycle, and
finally by the early cycle. Important differences were also found among the means for cultivar
groups, with the highest yields obtained in the “oakleaf green” and “lollo green” cultivar groups,
and the lowest in the “lollo red” group. However, there were important interactions between
cultivation cycle and varietal group. At this respect the highest yielding varietal type in the early
and intermediate cycle has been the “oakleaf green”, while for the late cycle has been the
“butterhead”. Differences in the performance and crossed interactions with the cultivation cycle
have also been found within varietal type. Some differences were also observed in the resistance
to early bolting. While no cultivar was prone to bolting in the early cycle, three of them (all of
the “oakleaf” groups) showed symptoms of early bolting in the intermediate cycle, and three
other (all of the “lollo” groups) in the late cycle. The results show that the important cultivar x
growing cycle interaction that takes place in the cultivation of lettuce under organic conditions
can be exploited by selecting the best cultivars for each growing cycle. The fact that the
materials of lettuce with better performance in each growing cycle are different, even within the
same cultivar group, supports the general view that the use of diversity can be used to a great
advantage in the production of organically grown vegetables.
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