Crop Science 43:426-429 (2003)
© 2003 Crop Science Society of America
NOTES
Morphological plasticity of chickpea in a semiarid environment
Pu-hai Liua,
Yantai Gan*,b,
Tom Warkentinc and
Cal McDonaldb
a Dep. of Water Resources Engineering, Gansu Agric. Univ., Lanzhou, Gansu, 730070 P.R. China
b Semiarid Prairie Agric. Res. Center, Agric. and Agri-Food Canada, Swift Current, SK, S9H 3X2 Canada
c Crop Development Centre, The Univ. of Saskatchewan, 51 Campus Drive, Saskatoon, SK, S7N 5A8 Canada
* Corresponding author (gan{at}em.agr.ca)
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ABSTRACT
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Chickpea (Cicer arietinum L.) is being rapidly adapted to the semiarid northern Great Plains, but little is known about the morphological responses of this annual grain legume to the dry environment. This study, conducted in southwestern Saskatchewan, examined the morphological plasticity of three market classes of chickpea by growing the crop at four plant population densities. Chickpea grown at high (50 plants m-2) population density produced approximately half as many fertile pods per plant as those grown at low (20 plants m-2) density, but total number of pods per unit area increased with increasing plant population density. Large-seeded kabuli chickpea produced fewer pods per unit area, or <60% of that produced by small-seeded kabuli, and <50% of that by desi chickpea. Infertile pods accounted for 17 to 23% of the total pods for large-seeded kabuli, compared with 9 to 12% for small-seeded kabuli, and 6% for desi chickpea. The large-seeded kabuli produced <87 seeds for every 100 pods produced, whereas desi and small-seeded kabuli produced >110 seeds for every 100 pods. Consequently, the large-seeded kabuli chickpea produced <90% of seed yield per unit area than small-seeded kabuli and desi chickpea. As plant population increased from 20 to 50 plants m-2, the seed yield m-2 increased by 20% for desi and 27% for small-seeded kabuli, but only 17% for the large-seeded kabuli chickpea. In the semiarid northern Great Plains, seed yield potential of desi and small-seeded kabuli chickpea can be increased by increasing plant population density, whereas the seed yield of large-seeded kabuli can be improved by increasing percentage pod fertility.
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INTRODUCTION
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THE CURRENT EMPHASIS on soil heath, environmental quality, and economic innovation has stimulated significant changes in cropping systems throughout the northern Great Plains (Gan et al., 2001; Miller et al., 2002). In the driest agroecoregion which encompasses southwestern Saskatchewan, southeastern Alberta, and northern Montana, hereafter referred to as Agroecoregion 12 (Padbury et al., 2002), there is an increasing interest in growing alternatives to cereal crops (Miller et al., 2002). In Saskatchewan, for example, the area seeded to chickpea has increased from <6000 ha in 1995 to >400 000 ha in 2001, with >90% of which being concentrated in the dry regions of the Brown (Aridic Haploborolls) and Dark Brown (Typic Borolls) soil zones (Gan and Noble, 2000). Three market classes of chickpea (namely desi, large-seeded kabuli, and small-seeded kabuli) are currently grown in these regions (Anonymous, 2002). Large-seeded kabuli chickpea has an average seed weight between 440 and 550 mg seed-1, and small-seeded kabuli has an average seed weight of 200 to 300 mg seed-1. The seed coat of kabuli chickpea is thin with a creamy color. Relative to kabuli chickpea, desi chickpea has a seed size varying from 170 to 320 mg seed-1, depending on cultivars. The seed coat of desi chickpea is thicker and usually tan to dark brown colored. Chickpea is a new crop with highest economic values in the semiarid regions. Large-seeded kabuli chickpea priced at $580 to $800 Mg-1 and desi chickpea $350 to $550 Mg-1 in the last four (1998–2001) years, which was, respectively, 4.5 to 2.5 times the grain prices of hard red spring wheat (Triticum aestivum L.) during the same period of time. Like other annual grain pulses, chickpea is a crop suitable for cereal-pulse rotation systems (Gan et al., 2001). Durum wheat (T. turgidum L.) grown after chickpea increased the grain yield by 5 to 10% and grain protein concentration by 6 to 16% as compared with durum wheat grown after spring wheat.
Chickpea has been grown in semiarid regions of the world for hundreds of years (Kumar and Abbo, 2001). This annual legume was recently introduced to the semiarid northern Great Plains and is being rapidly adopted by producers (Gan and Noble, 2000), but little is known about the morphological characteristics and their responses to agronomic management practices. Knowledge on plant morphology is crucial in understanding the responses of the crop to growing conditions and in developing agronomic strategies to manage the crop. Information on plant plasticity is also useful in screening genotypes that will be better adapted to the semiarid environments. The objective of this study was to determine the morphological plasticity of three market classes of chickpea by determining pod development and seed formation as the crop was grown with different plant population densities.
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Materials and Methods
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This research project was conducted in 1999 and 2000 at the Agriculture and Agri-Food Canada Semiarid Prairie Agricultural Research Centre near Swift Current (50.2' N, 107.4' W). Soil was an Orthic Brown Chernozem (Aridic Haploboroll) with loam to silt loam texture and pH in water paste of 6.5 in the 0- to 15-cm soil depth. The experiment was set up as a factorial, randomized complete block design with four replicates. Three market classes of chickpea, (i) large-seeded kabuli (cv. CDC Xena and CDC Yuma), (ii) small-seeded kabuli (cv. CDC Chico and B-90), and (iii) desi (cv. Myles), were planted directly on wheat stubble with four target population densities: 20, 30, 40, and 50 plants m-2. The seed rates were determined according to seed size, preseeding germination, and an estimated field emergence rate of 70%. The precise seeding rates were accomplished by using a seed meter built in the drill which had been adapted for plot work. Each plot was 7.5-m long and consisted of 10 rows with a 20-cm row spacing. Seed was placed at 5- to 6-cm deep, with phosphorus fertilizer applied with the seed at a rate of 7.5 kg P ha-1. All plots received 5.5 kg ha-1 of an appropriately labeled soil implant Rhizobium inoculant for symbiotic N fixation. The Rhizobium inoculant was applied in the seed rows at planting. Weeds were controlled using a combination of preplanting or preemergent burnoff treatment with glyphosate and in-crop herbicide {metribuzin [4-Amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one]} applications. One to three applications of chlorothalonil were used at the initial flowering stage of chickpea, or when disease symptoms were visually detected on leaves or stems, to control blight, a foliar disease caused by Ascochyta rabiei. After seedling emergence was complete, plant counts were conducted in two 0.5-m2 quadrants per plot; one in the front of the plot, and the other in the back of the plot. At plant maturity, 10 individual plants were sampled at random from each plot for plasticity determination. In the laboratory, all pods were opened by hand and the number of seeds in each pod was counted. We separately recorded the number of pods bearing 0, 1, and 2 seed(s), and calculated the total number of seeds per 100 pods. Seed yield per plant was determined by weighing all seeds together for a whole plant. Data for the 10 individual plants were averaged for each plot. The center eight rows of each plot (9.2 m2) were harvested with a plot combine when the crop had dried sufficiently for satisfactory threshing. The seed samples were air-dried, cleaned, and weighed. Seed yields per unit area were calculated and presented on a dry weight basis. For each plot, mean seed weight was determined by weighing 200 subsampled individual seeds. The data were analyzed using the PROC MIXED procedure of SAS (SAS Institute, 1996), with blocks as a random effect, and chickpea market classes and plant population densities as fixed effects. A separate analysis was performed for each of the three market classes to determine the linear responses to plant population density. Differences among market classes were determined at each plant population level. The two cultivars in the large-seeded kabuli class, CDC Xena and CDC Yuma, responded to the treatments similarly, as did CDC Chico and B-90, the two cultivars in the small-seeded kabuli class. Therefore, the mean values of the two cultivars within the respective market class were used in the analysis. Crops performed similarly between 1999 and 2000, and the year x treatment interactions were not significant, therefore the data of the 2 yr were combined in the statistical analyses.
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Results and Discussion
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In both years, spring conditions were adequate for seedling emergence, and the growing season (May to August) precipitation (250 mm) was slightly above the 40-yr (1961–2000) long-term average. Consequently, all market classes of chickpea achieved an adequate plant establishment with the actual plant counts close to the targets (data not presented). The four levels of plant population treatments created different plant communities which allowed the determination of the morphological characteristics of the different chickpea classes.
Pod Production
Total number of fertile pods per plant decreased significantly as the plant population density increased from 20 to 50 plants m-2 (Table 1); these patterns were similar for all three market classes. Plants grown at the high (50 plants m-2) density produced approximately half as many fertile pods (per plant) as those grown at the low (20 plants m-2) population density. The decreased pod production with increasing plant population density was presumably due to plant-to-plant competition for resources, as indicated from the Australian studies conducted by Beech and Leach (1989) and Jettner et al. (1999). There were significant differences in pod production among the three market classes examined in the present study. Desi chickpea produced the highest number of fertile pods per plant, which was more than double the number of pods produced by large-seeded kabuli, and was 20% higher than those produced by small-seeded kabuli chickpea. More than 96% of the pods contained one seed in large-seeded kabuli, while the one-seeded pods accounted for 80% of the total fertile pods for desi chickpea, and 75% for the small-seeded kabuli. The rest of the fertile pods contained two seeds. The small-seeded kabuli had the highest percentage (26%) of pods containing two seeds, followed by desi chickpea (19%). The large-seeded kabuli chickpea had <4% of the pods producing two seeds. The large-seeded kabuli chickpea apparently had limited sink size for accommodating more than one seed per pod.
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Table 1. Pod production of three market classes of chickpea grown at different plant population densities in the semiarid environment of Saskatchewan, 1999 to 2000.
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The number of pods per unit area is the most important component contributing to final seed yields in annual pulse crops, including kabuli chickpea (Beech and Leach, 1989), desi chickpea (Jettner et al., 1999), faba bean (Vicia faba L.) (Marcellos and Constable, 1986), and lentil (Lens culinaris Medik.) (Siddique et al., 1998). In our study, the number of pods per unit area increased significantly with increasing plant population density for all three market classes (Table 1). For example, desi chickpea increased fertile pods per square meter by 28% as plant population density increased from 20 to 50 plants m-2. Similarly, the fertile pods m-2 increased by 10% for large-seeded kabuli, and by 25% for small-seeded kabuli chickpea, with the increasing plant population density. At a given plant population density, the large-seeded kabuli produced the lowest number of pods per unit area, which was <60% of the pods produced by small-seeded kabuli, and was <50% of the pods produced by desi chickpea. The differences in pod production among the three market classes became more pronounced as the crop was grown at a higher population density. For example, at 50 plants m-2, the large-seeded kabuli plots had 46% as many pods per square meter as desi plots, while at 20 plants m-2, the large-seeded kabuli plots had 53% as many pods m-2 as desi plots. These results clearly indicate that desi chickpea will produce more pods per unit area than kabuli chickpea regardless of growing conditions or the potential plant-to-plant competition. The large-seeded kabuli chickpea has a lower plasticity or weaker buffering capacity in adjusting pod production, particularly when the pulse is grown in an environment where growth resources are limited.
It was noteworthy that there was a high percentage of pods producing no seed in chickpea (Table 1). The large-seeded kabuli had the highest percentage pod infertility (17–23%), followed by the small-seeded kabuli (9–12%), with desi chickpea having the lowest (6%) percentage of infertile pods. With the increases of plant population density from 20 to 50 plants m-2, the percentage pod infertility increased significantly for the two kabuli market classes (P < 0.01), whereas desi chickpea had a consistently low percentage pod infertility across the different plant population densities. These observations indicate that, compared with desi chickpea, the large-seeded kabuli chickpea not only has a limited capacity of forming sinks (as indicated by lower total number of pods per unit area), but also has a weaker ability to fill the sinks they formed (as indicated by the higher percentage pod infertility).
Seed Formation, Weight, and Yield
There were large differences among three market classes in seed formation, weight, and yield (Table 2). The large-seeded kabuli plants produced <87 seeds for every 100 pods produced. In contrast, desi plants produced 110 to 114 seeds, and the small-seeded kabuli plants 110 to 117 seeds for every 100 pods they produced. Fewer number of seed per pod for large-seeded kabuli plants was primarily due to the higher percentage (17–23%) of pods that failed to fill (Table 1), whereas the greater number of seed per pod for desi and small-seeded kabuli chickpea was due to a larger proportion (6–14%) of pods containing two seeds regardless of plant density. These results indicate that for desi and small-seeded kabuli types, the number of seeds per unit area can be increased by increasing plant population density; whereas for the large-seeded kabuli type, the number of seeds per unit area can be increased by promoting pod filling to reduce the percentage pod infertility.
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Table 2. Seed formation and yields for three market classes of chickpea grown at different plant population densities in the semiarid environment of Saskatchewan, 1999 to 2000.
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Mean seed weight of large-seeded kabuli was >430 mg seed-1 regardless of plant population density (Table 2). Mean seed weight of the small-seeded kabuli was nearly half the seed weight of the large-seeded kabuli, but was 25% heavier than desi-type seed. Plant population density did not influence the mean seed weight for any of these chickpea classes. Studies conducted elsewhere have also demonstrated that plant population density has none or little influences on mean seed weight in chickpea (Siddique et al., 1984; Beech and Leach, 1989; Saini and Faroda, 1998).
In contrast to mean seed weight, the seed yield per plant decreased significantly (P < 0.01) as plant population density increased from 20 to 50 plants m-2, for all three market classes (Table 2). There were crop type x plant population interactions in seed yield per plant. At the low (20 plants m-2) population density, desi type produced greater (30%) seed yield per plant than kabuli types, whereas at the higher population densities (>30 plants m-2), seed yield per plant did not differ among them. When grown in a low plant population density, desi chickpea produced the highest number of pods with lowest rate of pod-fill failure, resulting in highest seed yield per plant. Although the large-seeded kabuli chickpea had the highest mean seed weight, it did not compensate the potential yield loss due to fewer number of pods per plant and great (>17%) percentage pod-fill failure.
The seed yield per unit area is a combination of plant population, pod production, seed formation, and seed weight. Overall, the seed yield per unit area responded positively to plant population densities for all three classes (Table 2). As plant population increased from 20 to 50 plants m-2, the seed yield per square meter increased by an average of 20% for desi, 17% for large-seeded kabuli, and 27% for the small-seeded kabuli chickpea. At a given plant population density, desi and small-seeded kabuli chickpea produced similar seed yields per square meter, which was 9 to 15% higher than that produced by the large-seeded kabuli chickpea. The large differences in seed yield per square meter among the three market classes were primarily due to fertile pods per unit area (Table 1) where the large-seeded kabuli produced <60% as many fertile pods as those produced by small-seeded kabuli, and <50% of the pods produced by desi chickpea. In addition, the large-seeded kabuli plants produced fewer (26%) seeds per pod than the other two.
Our results are in agreement with those found elsewhere in the world. Saini and Faroda (1998) reported seed yield increases of kabuli chickpea up to 36% with plant population increases from 20 to 35 plants m-2 in semiarid northern India. Doubling kabuli chickpea plant population resulted in a 52% yield increase in a Mediterranean-type environment in Jordan (Kostrinski, 1974). Similarly, the seed yield of desi chickpea increased with increases of plant population from 33 to 50 plants m-2 in northern Syria (Singh and Saxena, 1996). In a subtropical region of Australia, Beech and Leach (1989) showed that a plant population of 40 plants m-2 was required to obtain maximum seed yields. In semiarid southwestern Australia, Jettner et al. (1999) found that a plant density of 50 plants m-2 was adequate for desi chickpea grown in low-yielding (
1.0 Mg ha-1) areas, but a plant density up to 70 plants m-2 was needed in high-yielding (>1.5 Mg ha-1) environments, for maximum seed yield and economic returns. Leach and Beech (1988) observed that annual pulses grown at high population density had a more rapid canopy cover in a relatively short period of time, allowing the plants to intercept more light early in the season than crops grown at low population density. The increased radiation interception with high plant population critically increases the efficiency of photosynthesis, provided that other factors such as soil water do not limit crop growth. Conversely to the above observations, Siddique et al. (1984) found no seed yield response to plant population density when chickpea was grown on sandy soils in a low rainfall Mediterranean-type environment of southern Australia. Low water holding capacity of sandy soils provided no benefits to chickpea plants grown at high densities in which plant-to-plant competition for available water was strong. When grown on the water-limited sandy soils, chickpea plants produced fewer branches at the high population than at the low population density. However, none of the published research (described above) has determined the detailed morphological plasticity of different market classes of chickpea. Furthermore, there is virtually no information available regarding the effect of plant population density on seed yield components of chickpea grown in no-till systems of the semiarid northern Great Plains. Our research clearly indicates that all three market classes of chickpea can be well adapted to the Agroecoregion 12 (Padbury et al., 2002). The seed yields of desi and small-seeded kabuli chickpea can be increased by increasing pod production per unit area via increasing plant population density, whereas the seed yield potential of large-seeded kabuli chickpea can be increased by reducing the proportion of infertile pods. These goals of maximizing chickpea seed yield in the semiarid northern Great Plains, more specifically in the Agroecoregion 12, are achievable through use of optimal agronomic management to promote pod production and decrease pod infertility.
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ACKNOWLEDGMENTS
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We acknowledge the excellent technical assistance of Greg Ford, Ray Leshures, Lee Poppy, and Ginny Cooke. The financial support of this research was provided by Saskatchewan Pulse Growers, the Agricultural Development Fund of Saskatchewan Agriculture and Food, and the Matching Investment Initiative of Agriculture and Agri-Food Canada. We also gratefully acknowledge Dr. Herb Cutforth and Dr. Elmer Stobbe for reviewing the manuscript.
Received for publication December 18, 2001.
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ABSTRACT
INTRODUCTION
