Location: Crop Improvement and Protection Research
Title: Baby leaf lettuce germplasm enhancement: developing diverse populations with resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vitians Authors
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 2013
Publication Date: January 8, 2014
Citation: Hayes, R.J., Trent, M.A., Mou, B., Simko, I., Gebben, S.J., Bull, C.T. 2014. Baby leaf lettuce germplasm enhancement: developing diverse populations with resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vitians. HortScience. 49:18–24. Interpretive Summary: Baby leaf lettuce cultivars with resistance to bacterial leaf spot (BLS) caused by the bacteria Xanthomonas campestris pv. vitians (Xcv) are needed to reduce crop losses and increase the sustainability of lettuce production. In cultivars that are susceptible to the disease, black watery spots appear on the leaves, which may coalesce into large patches. The disease lowers the quality and storage life of lettuce. We conducted experiments to determine which commercially available baby leaf lettuce cultivars possess BLS resistance. Greenhouse grown seedlings were given the BLS disease by spraying them with Xcv. These experiments found high disease severity in red leaf and red romaine cultivars. Based on this finding, we mated the lettuce cultivars Batavia Reine des Glaces and Eruption to develop a population for selection of lettuce with red colored leaves and resistance to BLS. Batavia Reine des Glaces is resistant to BLS, but is not suitable for commercial production. Eruption is a commercially useable red colored baby leaf cultivar that is susceptible to BLS. Progeny from this mating were grown in the greenhouse and sprayed with Xcv to cause BLS. Only resistant plants, those with less severe BLS disease than Eruption, and with red colored leaves were saved and allowed to flower and produce seeds of the next generation. Two generations of BLS disease resistance evaluation, selection, and seed production were conducted to develop two red colored lettuce populations with BLS resistance equal to Batavia Reine des Glaces. The populations were grown in two field experiments where they were determined to be susceptible to the insect pest leafminers and the fungal disease downy mildew. The shelf-life of packaged salad prepared from these populations is commercially acceptable. These populations can be used by private and publically employed lettuce breeders to select lettuce cultivars with BLS resistance and good salad shelf-life.
Technical Abstract: Baby leaf lettuce cultivars with resistance to bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vitians (Xcv) are needed to reduce crop losses. The objectives of this research were to assess the genetic diversity for BLS resistance in baby leaf lettuce cultivars and to select early generation populations of lettuce with BLS resistance. Greenhouse experiments using artificial Xcv inoculations were conducted to assess BLS resistance in 35 cultivars of ten lettuce types used in baby leaf production, and in F2 through F3:4 progeny from Batavia Reine des Glaces (BLS resistant, green leaf color) × Eruption (BLS susceptible, red leaf color). Higher disease severity was identified in red leaf and red romaine cultivars compared to other types, indicating the need to target these types for resistance breeding. Selection for BLS resistance and red colored leaves was therefore conducted among 486 F2 plants, 38 F2:3 families, and two populations of F3:4 families from Batavia Reine des Glaces × Eruption. Two populations were identified with uniform levels of BLS resistance equivalent ‘Batavia Reine des Glaces’, variable leaf morphology and color. These populations can be used by private and publically employed lettuce breeders to select for diverse types of lettuce cultivars suitable for baby leaf production and with BLS resistance.