An Evaluation of Solanum Nigrum and S. Physalifolium Biology And
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Lincoln University Research Archive An evaluation of Solanum nigrum and S. physalifolium biology and management strategies to reduce nightshade fruit contamination of process pea crops. _________________________________________ A thesis submitted in partial fulfilment of the requirements for the degree of Degree of Master of Applied Science at Lincoln University by S.L. Bithell _________________________________________ Lincoln University 2004 i Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science. An evaluation of Solanum nigrum and S. physalifolium biology and management strategies to reduce nightshade fruit contamination of process pea crops. By S.L. Bithell The contamination of process pea (Pisum sativum L.) crops by the immature fruit of black nightshade (Solanum nigrum L.) and hairy nightshade (S. physalifolium Rusby var. nitidibaccatum (Bitter.) Edmonds) causes income losses to pea farmers in Canterbury, New Zealand. This thesis investigates the questions of whether seed dormancy, germination requirements, plant growth, reproductive phenology, or fruit growth of either nightshade species reveal specific management practices that could reduce the contamination of process peas by the fruit of these two weeds. The seed dormancy status of these weeds indicated that both species are capable of germinating to high levels (> 90%) throughout the pea sowing season when tested at an optimum germination temperature of 20/30 °C (16/8 h). However, light was required at this temperature regime to obtain maximum germination of S. nigrum. The levels of germination in the dark at 20/30 °C and at 5/20 °C, and in light at 5/20 °C, and day to 50 % germination analyses indicated that this species cycled from non- dormancy to conditional dormancy throughout the period of investigation (July to December 2002). For S. physalifolium, light was not a germination requirement, and dormancy inhibited germination at 5/20 °C early in the pea sowing season (July and August). However, by October, 100% of the population was non-dormant at this test temperature. Two field trials showed that dark cultivation did not reduce the germination of either species. Growth trials with S. nigrum and S. physalifolium indicated that S. physalifolium, in a non-competitive environment, accumulated dry matter at a faster rate than S. nigrum. However, when the two species were grown with peas there was no difference in dry matter accumulation. Investigation of the flowering phenology and fruit growth of both species showed that S. physalifolium flowered (509 °Cd, base temperature (Tb) 6 °C) approximately 120 °Cd prior to S. nigrum (633 °Cd). The fruit growth rate of S. nigrum (0.62 mm/d) was significantly faster than the growth rate of i S. physalifolium (0.36 mm/d). Because of the earlier flowering of S. physalifolium it was estimated that for seedlings of both species emerging on the same date that S. physalifolium could produce a fruit with a maximum diameter of 3 mm ~ 60 °Cd before S. nigrum. Overlaps in flowering between peas and nightshade were examined in four pea cultivars, of varying time to maturity, sown on six dates. Solanum physalifolium had the potential to contaminate more pea crops than S. nigrum. In particular, late sown peas were more prone to nightshade contamination, especially late sowings using mid to long duration pea cultivars (777-839 °Cd, Tb 4.5 °C). This comparison was supported by factory data, which indicated that contamination of crops sown in October and November was more common than in crops sown in August and September. Also, cultivars sown in the later two months had an ~ 100 °Cd greater maturity value than cultivars sown in August and September. Nightshade flowering and pea maturity comparisons indicated that the use of the thermal time values for the flowering of S. nigrum and S. physalifolium can be used to calculate the necessary weed free period required from pea sowing in order to prevent the flowering of these species. The earlier flowering of S. physalifolium indicates that this species is more likely to contaminate pea crops than is S. nigrum. Therefore, extra attention may be required where this species is present in process pea crops. The prevention of the flowering of both species, by the maintenance of the appropriate weed free period following pea sowing or crop emergence, was identified as potentially, the most useful means of reducing nightshade contamination in peas. Keywords: Pisum sativum, Solanum nigrum, Solanum physalifolium var. nitidibaccatum, weed, dormancy, germination, thermal time, flowering, fruit growth. ii Table of contents Abstract ............................................................................................................................i Table of Contents............................................................................................................ iii List of Tables.................................................................................................................. vii List of Figures..................................................................................................................x List of Abbreviations ...................................................................................................... xii List of Appendices ........................................................................................................ xiii Chapter 1 General introduction .......................................................................................1 1.1 The problem of nightshade contamination of process peas.............................1 1.2 Justification ......................................................................................................2 1.3 Research objectives.........................................................................................4 Chapter 2 : Literature review ..........................................................................................5 2.1 Introduction ......................................................................................................5 2.2 Production of process peas..............................................................................5 2.2.1 Production of organic process peas.....................................................5 2.2.2 Contamination of process peas ...........................................................6 2.3 Weed management in process peas................................................................9 2.3.1 Organic weed management.................................................................9 2.3.2 Recommended weed management in organic pea crops....................9 2.3.3 Weed research relevant to organic pea production ...........................10 2.3.4 Germination reduction strategies.......................................................11 2.4 Dark cultivation...............................................................................................12 2.4.1 Theory of dark cultivation...................................................................12 2.4.2 Evaluations of dark cultivation ...........................................................14 2.5 The target weeds ...........................................................................................17 2.5.1 Taxonomy of the target weeds...........................................................17 2.5.2 Solanum nigrum biology and ecology................................................18 Germination requirements - temperature...........................................18 Germination requirements - light .......................................................20 Germination requirements - moisture ................................................21 Seasonal emergence.........................................................................22 Proportion of the seed bank to emerge, and seed viability................22 Emergence depth ..............................................................................23 Cultivation effects ..............................................................................23 Dormancy ..........................................................................................23 Plant growth.......................................................................................24 Development of flowers, fruit and viable seeds .................................24 2.5.3 Solanum physalifolium biology and ecology ......................................26 Solanum physalifolium.......................................................................26 Solanum sarrachoides.......................................................................27 2.6 Summary........................................................................................................28 Chapter 3 Processing factory contamination records – analysis for causal factors ..........................................................................................................29 3.1 Introduction ....................................................................................................29 3.2 Materials and methods...................................................................................29 3.3 Results ...........................................................................................................30 3.3.1 Monthly sowing date effects...............................................................30 3.3.2 Cultivar