title: The effects of fertilisers, particularly foliar applied, onthe potato plant's tolerance of attack by the potato cystnematodes, <i>Globodera rostochiensis</i> and <i>G. pallida</i>
Creators: name: Grove, Ivan Geoffrey
Publisher: name: The Open University
Year: 1999

description: Potato cyst nematodes, PCN, cause major yield loss in commercial potato production. One of the mechanisms of yield loss cited is a reduction in the uptake of the major nutrients nitrogen (N), phosphorus (P) and potassium (K). For the work described in this thesis, it was hypothesised that nutrient application via the foliar route could by-pass the PCN-damaged plant root system, ameliorate the PCN-induced nutrient deficits and increase plant yield and tolerance of PCN attack. None of the three nutrients investigated (N, P, K) was individually shown to limit plant growth or yield of PCN-infected plants. However, plant nutrient concentrations were affected by PCN-infection: N and K concentrations were reduced by 30 days after planting (DAP); N and P concentrations were significantly reduced by 56 to 61 DAP; but N and P were significantly greater in plants by 104 DAP. PCN-infection also significantly retarded plant emergence, and reduced plant growth and yield in all investigations. Applying placed liquid fertiliser increased the plant nutrient concentrations but did not increase tuber yield significantly. Applying one third of the recommended fertiliser quantity as foliar applied nutrients effectively replaced seedbed application, increased the nutrient concentrations within the plants and gave equivalent or higher tuber yields than in plants receiving all of the fertiliser in the seedbed. Applying all of the recommended quantity of N in the seedbed at planting did not increase early plant growth, although it did redress some of the PeN-induced nutrient deficits, and appeared to aggravate the yield loss associated with PCN infection. Applying foliar N on five occasions, at approximately 14-day intervals, produced small but consistent yield improvements by increasing ground cover and leaf area index. Yield improvements were also seen where applications included either foliar K within the foliar N application, or when one early foliar P application was made with the first of four or five foliar N applications. Applying foliar P alone on four occasions at approximately 5-day intervals from early post-emergence, or five occasions at approximately 14 day intervals from tuber initiation, reduced plant growth and yield. However, even where nutrient concentrations within PCN-infected plants were increased to the same level as, or greater level, found in relatively PCN-free plants, no significant plant growth benefits occurred. Therefore, it is postulated that a separate mechanism, i.e. phytohormone imbalance, may be solely or additionally responsible for the poor growth of PCN-infected plants. Field and glasshouse investigations showed contrasting effects of nutrients, especially foliar-applied, and nematicide applications, and highlighted the greater suitability of field experimentation for these types of investigation. The Diagnosis and Recommendation Integrated System (DRIS) was investigated as an alternative diagnostic tool to aid the identification of nutrient disorders. Although no remedial nutrient applications were made as a result of the findings from this method, it suggested that P was most limiting for early plant growth and, in contrast to the statistical analysis which showed no limitations, K was most limiting for plant growth later in the season. In conclusion, it is suggested that foliar nutrient applications can benefit the growth, yield and tolerance of PCN-infected plants, but that plant tolerance may benefit further if nutrient applications match the requirements of the plant as shown by plant nutrient analyses.