Rootzone pH affects nutrient availability for plants. Hydroponic leafy greens are grown in nutrient solutions with pH 5.5 to 6.5. Lower pH may inhibit plant growth, whereas pathogenic oomycete growth and reproduction may be mitigated. General understanding of pH effects on nutrient availability suggests likely toxicity and deficiency of specific micronutrients. We hypothesized that if adjustments are made to the micronutrient concentrations in solution, plants will grow in lower-than-conventional pH without nutrient disorders, while oomycete disease incidence and severity may be reduced. To develop a new nutrient solution management strategy, we examined pH of 4.0, 4.5, 5.0, and 5.5 with or without micronutrient adjustments for growing two cultivars of basil plants Dolce Fresca and Nufar in a greenhouse hydroponic deep-water culture (DWC) system. Micronutrient adjustments included reduced concentrations of copper, zinc, manganese, and boron by one-half and doubled molybdenum concentration. Plants harvested 20 to 28 days after transplanting did not show significant effects of pH or the micronutrient adjustment. Phosphorus, calcium, magnesium, sulfur, boron, manganese, and zinc concentrations in leaves significantly declined, while potassium and aluminum concentrations increased with decreasing pH. However, these changes and therefore micronutrient adjustments did not affect basil plant growth significantly. ‘Nufar’ basil plants were then grown in a growth chamber DWC system at pH 4.0 or a conventional 5.5 with and without inoculation of Pythium aphanidermatum zoospores. Fourteen days after inoculation, P. aphanidermatum oospore production was confirmed only for the inoculated plants in pH 5.5 solution, where a significant reduction of plant growth was observed. The results of the present study indicate that maintaining nutrient solution pH at 4.0 can effectively suppress the severity of root rot caused by P. aphanidermatum initiated by zoospore inoculation without influencing basil growth.
Daniel P. Gillespie, Chieri Kubota, and Sally A. Miller
L. Mark Lagrimini, Jill Vaughn, W. Alan Erb, and Sally A. Miller
Lignin composition in leaf, fruit, and fruit outer epidermis of transgenic tomato (Lycopersicon esculentum Mill.) plants that overproduce the enzyme tobacco anionic peroxidase (TobAnPOD) was analyzed. This enzyme may catalyze the polymerization of cinnamyl alcohols into lignin in tobacco (Nicotiana tabacum L.); therefore, we predicted that its presence in the transformed tissue would increase lignin levels in healthy and wounded tissue. Lignin levels in healthy plants increased by 20% in leaf, 49% in fruit, and 106% in fruit outer epidermal tissue. Mature-green fruit were aseptically wounded and incubated in darkness for up to 7 days. Soluble phenols in wounded transgenic fruit increased by more than 300% hut changed little in control fruit. As with soluble phenols, lignin content in wounded transformed fruit increased by more than 20-fold hut increased less than two-fold in control fruit. Transgenic seedlings overproducing TobAnPOD were screened for susceptibility to several pathogens, but resistance did not increase. Possible TobAnPOD roles in lignin biosynthesis, phenol metabolism, stress response, and disease resistance are discussed.
Anna L. Testen, Delphina P. Mamiro, Hosea D. Mtui, Jackson Nahson, Ernest R. Mbega, David M. Francis, and Sally A. Miller
Tomato is an important cash crop in many developing countries. However, smallholder farmers often lack access to improved cultivars and breeding programs to develop locally adapted cultivars are limited. Participatory crop improvement (PCI) approaches can be used to increase farmer access to improved cultivars. In this project, we used the mother and baby trial (MBT) design to introduce and evaluate tomato cultivars in three villages in the Morogoro Region of Tanzania. Mother trials were conducted in seven environments within the three villages, and variance partitioning revealed significant genetic effects for all traits measured with h 2 ranging from 0.74 to 0.90 for yield and disease reaction, respectively. In baby trials, farmers provided qualitative rankings of cultivars for 16 characteristics, including vigor, yield, harvest period, diseases, insect damage, fruit quality, and salability. Results from baby trials indicated that introduced cultivars were locally acceptable to farmers, except for traits related to marketability. Outcome Mapping was used to evaluate progress in each of the three villages and results suggested that high stakeholder participation levels could predict future adoption of introduced cultivars. Our findings provide a framework for evaluating, selecting, and breeding tomato and other horticultural crops in developing countries using the MBT design for PCI.