Developing field pea varietal blends for higher yields and pest suppression
To determine the optimum ratio of leafed to semi-leafless pea to maximize yield, across different genetic backgrounds, locations and years.
The primary production and secondary processing of field pea makes a significant contribution to Saskatchewan’s economy annually. Field pea has two distinct leaf morphologies: a leafed-type (LV) with leaflets extending from the stipule; and a semi-leafless (SL) type, with tendrils extending from their stipules. Semi-leafless types exhibit better lodging resistance than leafed types, which improves harvestability and crop yields under certain environmental conditions. For this reason, semi-leafless varieties have displaced leafed varieties; however, leafed varieties are still favored for forage production. Previous research has indicated that when lodging is prevented, leafed varieties can out-yield semi-leafless varieties. Thus, the blending of leafed with semi-leaf varieties may overcome lodging issues, resulting in higher yields. To test this hypothesis, near isogenic leafed lines of 4 high-yielding semi-leafless varieties (Amarillo, Dakota, Centennial, and Striker) were bred. Two field studies were conducted from 2017-19; the first, comparing the performance of near-isogenic blends of 75:25 SL:LV to non-isogenic blends (same SL:LV proportions) as well as to SL and LV monocultures. The second study investigated the blending ratio of LV to SL required to optimize light interception and yield, as well as to reduce lodging and disease severity. A third study used digital imaging to measure field pea height and assess lodging, and compared these measurements to ground measurements. In study one, Amarillo, Dakota, and Striker blends yielded similarly to the LV and SL monocultures; whereas, the Centennial blends yielded 9% lower than the SL monoculture. LV monocultures had lower lodging height indexes (higher lodging) than the LV:SL blends and their SL monoculture counterparts. Blends of Centennial, Amarillo, and Striker had similar lodging height indexes as SL monocultures; however, the lodging height index of Dakota blends was 9% lower than the SL monoculture, indicating slightly higher lodging with the blend. Blends of near-isogenic pairs performed similarly to non-isogenic pairs in terms of lodging height index, disease severity, biomass production, and crop yield. In study two, SL:LV ratios up to 67/33 of provided a 1.4%-7.4% yield increase compared to SL (100/0) monocultures; however, this was variety dependent. The lodging height index of LV:SL blends was similar to the SL monoculture provided the LV proportion was less than 33%. The nDSM, a canopy height measurement derived from digital images, correlated highly with manual measurements of crop height (r > 0.80). Lodging estimates from digital imagery were able to distinguish treatment differences with more precision than manual ground measurements. The peak nDSM and maximum nDSM provided fair predictions of final yield (r = 0.51). The benefits of blending semi-leafless and leafed varieties was small, and the proportion of leafed material in the blend should not exceed 33%. In conclusion, the yields of semi-leafless and leafed blends were similar to semi-leafless parent indicating that large yield gains should probably not be expected by blending semi-leafless and leafed pea varieties.
- Blending of leafed and semi-leafless near-isogenic and non-isogenic lines improved lodging resistance compared to a leafed monoculture. Lodging resistance of the blends were generally similar to the semi-leafless monoculture; however this was variety specific.
- To optimize lodging resistance in a blend, the proportion of the leafed component should not exceed 33%.
- Overall the yield of pea varietal blends was similar to the semi-leafless parent. Blends, in which the proportion of the leafed component was 17 to 33%, provided very small (1.4 to 7%) yield increases over the highest yielding semi-leafless monocultures; however, this was also variety dependent and often did not differ significantly from the yield of the semi-leafless parent.
- The digital estimates of height loss over time were able to differentiate lodging differences between treatments with higher precision than ground estimates.
- Estimates of peak nDSM, a canopy height measurement derived from digital images, and maximum nDSM provided a fair prediction of crop yield.