Research Objective
To determine whether heat stress coupled with drought stress during flowering cause high rate of flower abortion in field pea.
Objective 4To determine the difference in the composition of rhizobacterial communities associated with various pulse crops and to relate these differences with the functionality of the rhizobacterial communities.
To determine whether heat stress coupled with drought stress during flowering cause high rate of flower abortion in field pea; to assess most sensitive stages at which the high-temperature and water stress occur to the pea plants; to evaluate the relationship between pod production and seed set and grain yield in pea cultivars released from 1970s to the most recent years; to determine the difference in the composition of rhizobacterial communities associated with various pulse crops and to relate these differences with the functionality of the rhizobacterial communities.
Declining pea yields in the drier southwest has been threatening many pea producers, and some pea producers have been calling for urgent solutions in order to sustain pea production and continuously take the great advantage pulse crops have been offering to Saskatchewan farmers. The findings from this research project may have direct benefits to Saskatchewan producers as this information and knowledge can be used to develop some tactics and practices to tackle pea yield decline.
Several hypotheses have been proposed to tackle the issue of the yield decline. Among the hypotheses is that heat stress due to warming climates coupled with water stress during the reproductive growth period may cause the reduction of the number of pods per plant that lowers the number of seeds per pod, thus decreasing pea yield. Also, crop rotations may have a significant impact on soil microbial communities, which, in turn, may affect crop performance.
A controlled environment study was conducted in 2012 and 2013 using the growth chamber facilities at the AAFC Research Centre, Swift Current. Three modern growth chambers were set at day/night temperature of 20/16 (no heat stress), 28/16 (moderate stress), and 35/16 (high stress) conditions, five pea varieties released in early days (1970s, 1980s, 1990s) and those released in recent years were evaluated under low- and high-water stress conditions. During the four weeks of pea flowering, heat- and water-stress treatments were imposed to stress pea plants for short- (one week) and long- (two weeks) period. Flower abortion rate, fertility ratio, pods per plant, seeds per pod, weight per seed, and seed-fill capacity were determined. The experiment was repeated twice in order to make sound conclusions.
The second study was a field experiment conducted at the Research Centre in Swift Current, which was in combination with a four-year pulse crop rotation field study, funded by Pulse Cluster project. In this trial, a total of 15 different cropping sequence/frequency rotation systems are evaluated for their yield performance, carbon, and nitrogen dynamics, weed and disease issues, and economics. Soil samples were taken from field plots during pulse flowering and also after pulse harvest. The composition of rhizobacterial communities associated with various pulse crops was determined, and the functionality of the rhizobacterial communities in relation to pulse rotation was evaluated.
The project showed that there was a general trend that high temperature stress had a strong negative impact on seed yield compared to water stress. All pea cultivars had a similar response to the stresses imposed during the flowering. The newer cultivars like CDC Meadow had the same tolerant level to heat and water stresses as the cultivars released from 1970s like Trapper. There was a significant linear relationship between seed yield and the number of fertile pods per plant. As the number of fertile pods per plant increased, the pea seed yield increased linearly. As well, early-stressed plants had an opportunity to recover from the stress, leading to more live flowers, while the stress at the mid-flowering stage caused more detrimental damage causing a high rate of flower abortion.
Results showed that without heat or water stress (check), pea plants produced an average seed yield of 6.02 grams per plant (or 4800 kg/ha). A short period of stresses (7 days during the flowering) decreased seed yield significantly: with the early-flowering stresses, the cultivar Victoria produced the highest seed yield at 5.1 grams per plant (or 4000 kg/ha), and the cultivar Carneval the lowest at 4.2 grams per plant (or 3360 kg/ha). An interesting observation was that heat stress imposed at the early-flowering stage did not reduce the number of pods per plant, and instead, the heat stress at that particular stage actually increased the number of pods per plant especially for the cultivars Trapper and Victoria. These two cultivars recovered rapidly from the early-stage stress.
Overall, a seven day period of day temperature of 35°C can severely limit pea yield. A 7-day period of day temperature of 28°C can also limit pea yield under the conditions of suboptimal soil moisture. Mid-flowering is a more sensitive stage than early flowering in pea. Larger genetic variation in the sensitivity of pea cultivars suggests there is a huge opportunity for breeding stress tolerant pea cultivars through genetic manipulation.
This field crop rotation experiment provided strong evidence that the soil bacterial community in a pulse field can promote plant growth and may be a component of the so-called “rotation effect”, which varies in magnitude in different crop rotation systems. The structure and functionality of the rhizobacterial community varies with plant genotypes, therefore, the selection of crop genotypes for their ability to improve soil biological quality may increase the productivity of cropping systems. The project also showed that environmental factors, such as moisture availability, however, appeared as a major driver of soil bacterial community dynamics, whose influence can override the effect of plant genotype. The strength of a rotational effect of pulses on soil biological quality is modulated by the abundance of precipitation.
The project shows that there is a general trend that high temperature stress has a strong negative impact on pea yield compared to water stress. All pea cultivars evaluated in the study expressed a similar response to the stresses imposed during flowering. Mid-flowering is a more sensitive stage than early flowering. The genetic variation in the sensitivity of pea flowering to heat stress offers an opportunity to develop new pea cultivars with improved heat tolerance; this could be done through genetic manipulation.
Pea is the #1 pulse crop in Western Canada, and the sustainable production of field pea is critical to maintain the long-term health of the pulse industry. Among the over 2.5 million acres of field pea grown annually in Saskatchewan, two thirds are produced in the Dark Brown and Brown soil zones. The findings from this project will directly benefit Saskatchewan producers by developing tactics and practices in tackling yield decline. For example, the project shows that as short as 7 days under 28/16oC degrees during flowering can significantly increase flower abortion rate and decrease pea yield. A simple approach is to seed pea on an earlier date allowing the plants to avoid the hot summer days during the flowering, helping minimize the flower abortion, enhance the fertile pods, and increase pea yield. Further, by using optimized crop rotation systems found in this project, producers can utilize the soil biological functions associated with the microbial communities in pulse-based rotation systems. Root rhizosphere in pea plants seems to offer the best benefits to the succeeding cereal crops. The genetic variation in the sensitivity of pea varieties offers an opportunity for pea genetic improvement.