Factors affecting seed vigour in field peas (Pisum sativum L.)

This work investigated the relationship between agronomic treatment of the mother plant and the quality of seed produced as measured by both laboratory seed vigour tests and field emergence and yield in field peas (Pisum sativum L.). Although there are now recognised ISTA tests of seed vigour in garden peas, no such standard tests currently exist for field peas. In the first experiment, determinate (Beacon) and indeterminate (Whero) pea cultivars were grown under full sunlight or under 40 % shade from flowering on. In Experiment 2 they were grown from small or large seed and sown in September and November and grown with or without irrigation (Experiment 2, 1997/98). Finally the two cultivars were grown and desiccated with reglone at 70, 62, 53 and 33 % seed moisture content (SMC) and the seeds were harvested at 16 % SMC or were harvested from non-desiccated plant at 16 % SMC (Experiment 3, 1996/97). The field performance of seed collected from the above experiments was evaluated. In Experiment 1 the seed yield of Beacon was 23 % higher than that of Whero (277g/m2) mainly due to more seeds/pod. Both cultivars, grown under full sunlight produced 27 % more seed yield than plants grown under 40 % shade (272 g/m²). This was mainly associated with more pods/plant and a higher thousand seed weight. Seed germination (≥89 %) was little affected by cultivar .and light level. However, seed vigour was markedly affected by the both factors. Whero had higher vigour seeds than Beacon, especially as determined by seedling dry weight (11 - 28 mg vs 6 - 20 mg). Seeds from unshaded plants had greater vigour than those from shaded plants. This was shown by 1.4 - 7.1 mg higher mean seedling weight at germination before and after accelerated ageing (AA), a 4 - 17 % greater germination after AA and a 5 - 23 µS/cm/g lower electro conductivity in seed from unshaded plants. Smaller seed size and lower seed vigour of shaded peas were particularly evident in seeds from top pods of the plant. In Experiment 2, seed size of mother plants had no effect on crop establishment, seed yield and quality of the progeny. September sown peas produced greater seed yield than November sown peas, especially for Beacon (643 vs 314 g/m²). An increase in TDM in both cultivars and in seeds/pod in Beacon was associated with the seed yield increase. Irrigation increased the seed yield of September sown peas by 33 %. Irrigation also increased the seed yield of Beacon by 25 %, but had no effect on the seed yield of peas sown in November or of Whero. The increased seed yield was mainly associated with an increase in total dry matter. In both cultivars seed germination was high (99 - 100 %). At final harvest (18 % SMC) Beacon seeds from the November sowing, with irrigation, had the lowest vigour (EC of 12.8 µS/cm/g). There was no difference in seed vigour among the rest of the seed lots of both cultivars (EC of 5.3 - 7.8 µS/cm/g). Seed vigour differences as measured by AA test and seedling dry weight varied according to times of harvest. In Experiment 3, seed yield did not differ between cultivars but did differ among desiccation times. Desiccation at 33 or 40 % SMC did not reduce seed yield, thousand seed weight, germination or vigour in either cultivar. Desiccation at 53 % SMC did not reduce germination of either cultivar but it did reduce seed yield and vigour. Desiccation at 62 and 71 % SMC reduced both seed yield and quality. In all experiments high vigour seed lots emerged well while low vigour seed lots emerged poorly. Seed lots with a low field emergence also emerged more slowly, had a lower plant establishment, a lower leaf area index (LAI) and leaf area duration (LAD). The number of plants/m², at final harvest, from low vigour seed lots was reduced by 33-50 % down to 10 - 12 plants/m². This resulted in a lower TDM (362 - 408 g/m² vs 793 - 1087g/m²) and a reduction in seed yield (169 - 176 g/m² vs 407 - 534 g/m²). Sowing date affected emergence rate but had no effect on either TDM or on seed yield. The electro conductivity test had the highest potential as a laboratory based test to predict the field emergence of field pea seed. Further, the accelerated ageing test also has the potential to predict field emergence of field pea seed.