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Potato tuber quality management in relation to environmental and nutritional stress Stephen Harper QLD Department of Primary Industries and Fisheries Project Number: PT99052 PT99052 This report is published by Horticulture Australia Ltd to pass on information concerning horticultural research and development undertaken for the potato industry. The research contained in this report was funded by Horticulture Australia Ltd with the financial support of the potato industry. All expressions of opinion are not to be regarded as expressing the opinion of Horticulture Australia Ltd or any authority of the Australian Government. The Company and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this report and readers should rely upon their own enquiries in making decisions concerning their own interests. ISBN 0 7341 0903 2 Published and distributed by: Horticultural Australia Ltd Level 1 50 Carrington Street Sydney NSW 2000 Telephone: (02) 8295 2300 Fax: (02) 8295 2399 E-Mail: [email protected] © Copyright 2004 Queensland the Smart State Potato tuber quality management in relation to environmental and nutritional stress. Final report HAL project PT99052 April 2004 Stephen Harper Queensland Government DPI&F HAL project No. PT99052 Potato tuber quality management in relation to environmental and nutritional stress. Stephen Harper Queensland Government DPI&F Gatton Research Station LMB7 MS 437 Gatton 4343. 07 5466 2222 This report outlines the factors that cause and enhance symptoms of brown fleck in potato tubers. It also evaluates potential management strategies that reduce incidence of brown fleck. Date of completion April 26 2004 Any recommendations contained in this publication do not necessarily represent current Horticulture Australia policy. No person should act on the basis of the contents of this publication, whether as to matters of fact or opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication. 1 Contents Media Summary 3 Technical Summary 4 1. Introduction 7 2. Materials and Methods - General 10 3. The Effect of Temperature on the Incidence of Brown Fleck 12 4. Effects of Calcium and Boron on BF 25 5. Understanding Field Physiology of BF 32 6. Effects of Assimilate Supplementation on BF Incidence 42 7. Brown Fleck Microscopy and Phenology of Development 46 8. Technology Transfer 54 9. Recommendations 54 10. Acknowledgements 55 11. Literature Review 56 12. References 75 . 2 Media Summary The causes and management strategies for the potato tuber internal disorder brown fleck (BF) were evaluated. This disorder reduces potato growing profitability in problem regions and is a major cause of potato consumer dissatisfaction. Worldwide research on causes of BF and its solutions has not been substantiative. The results of this project show incidence and development of BF symptoms appear to be 2 separate processes. Initiation of BF relates to the death of specific sugar conducting cells in the tuber and as a consequence further severe cellular disruption occurs. There is a strong relationship between crops having high yield potential and high BF incidence, hence factors that favour rapid tuber growth also favour high BF incidence. In support of this BF incidence was increased specifically by elevated night temperature (but not day temperature) and vigorous crop foliage growth. High soil temperature enhanced symptom development. In minimising incidence of BF, growers need to prevent prolific canopy development, which can largely be achieved by ensuring that nutrient application and irrigation are not excessive. Early monitoring of tubers for the first evidence of BF incidence should be conducted which can form the basis for determining whether preventative measures are required. Short term weather outlooks could be used as a basis for determining whether imminent weather conditions would be favourable for rapid tuber growth; in particular, warm nights, mild sunny days and rain events. In the event that there is early evidence of BF and conditions are favourable for its development, the management of crop foliage should be considered. This can be achieved by potentially spraying defoliants or agents that might harden the crop up including copper or calcium. The maintenance of weed or vegetative cover at crop senescence should be encouraged so as to provide shade to soil and preventing excessive soil temperatures that favour enhancement of BF symptoms. Application of calcium or boron did not significantly or reliably reduce incidence of BF and based on this is not recommended as a means of controlling BF. These nutrients should nonetheless be applied at rates appropriate to meet normal growth requirements. The cause of the initial cell death requires further research and particularly in relation to varieties that are both susceptible and resistant to BF. As well as providing an understanding of BF causes at the cellular level this would form a basis for the breeding and developing of new varieties that are resistant to BF. Also further work is required to evaluate the potential of different defoliants or retardants and their rates and timing of application. 3 Technical Summary Temperature Results over the series of experiments demonstrate that elevated night time temperatures and high soil temperature dramatically increase the expression of BF. Elevated daytime temperatures did not greatly increase the expression of BF. Moderate temperature regimes (including mild days and warm nights) were most favourable to the development of BF and this was particularly evident in the 2000 experiment where plants exposed to a constant day/night temperature regime of 23/18oC exhibited BF incidence as high as that exhibited under a shorter exposure to 28/23oC. In contrast to the night temperature effect, high daytime temperature did not appear to greatly increase the incidence of BF. The effect was clearly demonstrated by comparing BF incidence under day night treatment temperature regimes of 28/23 oC and a 28/13 oC in the 2001 experiment. Incidence of BF was substantially higher at 28/23 oC compared with that in the 28/13 oC treatment and incidence was much greater under a 23/18 oC regime than under a 28/13 oC regime despite the mean treatment temperature being was the same. Tuber dry matter % (DM%) was not affected by diurnal temperature patterns but rather was related to overall heat exposure with higher temperature reducing DM%. Whereas the BF incidence was particularly related to warm night temperature DM% was more related to the heat units experienced by the plant. Albeit at low levels, BF was still observed in tubers of plants grown under a low day night temperature regime (18 /13 oC) suggesting that elevated temperature per se does not appear to be the sole critical factor in inducing the disorder. It appears that an expansion of BF symptoms occurs at higher temperature probably due to the increased activity of oxidising enzymes and greater assimilate supply to tubers. Tuber yield and BF A positive relationship existed between yield potential and incidence of BF where high yielding plants exhibited high incidence of BF. This is further confirmed by virtue of the positive correlation between plant foliage weight and incidence of BF. Plants with a greater amount of foliage exhibited higher BF incidence. This effect is likely to be indirect and related to the greater amount of foliage increasing assimilate supply to tubers. The issue of temperature and tuber growth and BF incidence is important since increased temperature not only increased BF but consistently increased tuber yield in each experiment. The microscopy studies highlight that increased carbohydrate supply and the inability of blocked phloem sieve cells to pass the extra sucrose to newly developing cells appears to be a major factor in the expansion of BF symptoms. Nutrition The presence of low incidence of BF in day night temperature treatments 18oC/13 oC suggested other factors may cause disorder. On this basis the effect of various rates of calcium 0-127 kg ha-1 and boron 0-5 kg ha-1 on BF incidence was evaluated. The effects of both Ca and B on incidence of BF were inconsistent and generally not 4 statistically significant. It is possible that any effect of either B or Ca on BF incidence is indirect through an inhibition of foliage growth, which would reduce the intensity of BF symptoms through reduced assimilate supply to tubers. There is no basis for making recommendations for application of Ca and B to reduce incidence of BF. Foliage management A series of field experiments was conducted to evaluate the effects of foliage removal on the incidence of BF. Removal and retarding of foliage generally reduced incidence of BF and shows good potential as a tool in minimising incidence of BF. The evidence presented suggests that growers should monitor potato crops for the first detectable incidence of BF and this can form the basis of a canopy management strategy. In addition, growers in regions where BF is a problem should attempt to grow crops a little on the hard side so that the proliferation of a vigorous canopy is not promoted. Various mechanisms for achieving this could be applied including use of defoliants or retardants, or restricting or withholding irrigation and not applying excessive nutrient application that favours foliage growth. A major trade off with removing foliage is the potential yield loss but early removal of only 25 % of leaf foliage does not appear to affect final yield. Further research is required to evaluate forms rates and timing of potential retardants. Supplementing assimilate Given that high night temperatures and a large plant foliage mass favoured BF symptoms two explanations were proposed. Firstly this set of circumstances could result in increased photosynthesis and assimilate supply to tubers or alternatively increased foliage respiration might have occurred leaving a deficit of assimilate to growing tubers and localised tuber cell death.

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