temperatures and rainfall variability are relatively high, ranging from 16.5°C to 24.9°C, and from 88.0% to 139.3%, respectively. As was the case with PC1, Ethiopia has a wide range of PC2 scores in close proximity, indicative of a wide habitat diversity, which is reflected in the diversity of the germplasm found there (Harlan, 1969).
In North America PC2 scores increase with latitude along the west coast, and from the Pacific North-west to the Northern Plains (Fig. 3.2b). Medium to navy blue zones in the north are particularly cold in winter, ranging from
−10.3°C to −1.8°C, despite their relative low altitude (322–810 m, Table 3.2a).
South America is characterized largely by low to medium PC2 scores, with rel- atively high rainfall variability (82.2–116.3%), and low summer temperatures (14.7–21.4°C) and altitudes (189–1222 m, Table 3.2b).
In Australia, the area for cultivating chickpea is characterized by intermedi- ate PC2 scores, increasing from east to west in the southern, Mediterranean-type region, and from south to north along the east coast. In the summer-dominant rainfall regions of the northern east coast, PC2 scores tend to increase from east to west. Altitudes and rainfall variability tend to be relatively low (50–612 m, 27.9–119.8%) within their respective PC2 categories.
This climate analysis demonstrates that while the world’s chickpea- growing regions can be grouped into four coarse rainfall and temperature categories (Mediterranean rainfall distribution, cool or warm climate; summer-dominant rainfall, cool or warm climate), there is a climatic diversity within and between regions captured by the sliding scale of PC1 and PC2 scores (Fig. 3.2a and b).
The rest of this chapter will discuss chickpea adaptation from an agroclimatic perspective.
Chickpea Adaptation: Stresses, Cropping Systems and Traits
regions of North America, and to a lesser extent, in subtropical Australia (Table 3.3). Only in extremely warm or isolated Mediterranean environments such as the Nile Valley or Chile, respectively, does ascochyta blight present less of a threat to chickpea production. Given the capacity of the disease to spread rapidly once it has established a foothold (Galdames and Mera, 2003), isola- tion is unlikely to remain an effective barrier for long. The fusarium wilt–root rot complex is the primary biotic stress of most of the summer-dominant rain- fall chickpea-growing regions (Table 3.3), and is estimated to be responsible for 10% annual yield loss in India (Singh and Dahiya, 1973). These diseases also occur in Mediterranean-type climates (Table 3.3), but are generally ranked behind ascochyta blight in terms of breeding priorities. Botrytis grey mould is another widely distributed disease of chickpea (Table 3.3), which causes significant damage in north-western South Asia, particularly from the northern Indian states to Nepal and Bangladesh (Gurha et al., 2003). Insect pests of chickpea can also be classified by region and climate (Table 3.3). Pod borer and bruchids are more significant in summer-dominant rainfall zones, while leaf miner is more common in the Mediterranean.
Cropping Systems
Chickpea-sowing strategies vary with environment so as to fit the crop into the farming system and minimize exposure to the prevalent stresses. The widest range of sowing strategies is found in the Mediterranean climates, depending on the relative intensity of the principal stresses (ascochyta blight, cold/frost and terminal drought; Table 3.3).
Autumn-sown rainy season crop maturing in late spring or early summer This is the system of choice for regions with relatively warm winters and low Ascochyta pressure (low–medium PC1 and medium–high PC2) because it capi- talizes on within-season rainfall and minimizes exposure to terminal drought. In WANA this system is traditionally used in the Nile Valley (Masadeh et al., 1996) and the warmer areas of Iran (entezari system; Sadri and Banai, 1996). It is interest- ing to note that these areas fall into the high-stress zone on the upper left quadrant of Fig. 3.2, which is characterized by the lowest, most winter- dominant annual rainfall, and the highest summer temperatures of the world’s chickpea-growing regions. In both countries chickpea is grown with supplemental irrigation in these areas to ameliorate drought stress. Recently winter sowing and drip- irrigation has been adopted by ~90% of Israeli chickpea farmers (S. Abbo, The Hebrew University of Jerusalem, 2006, personal communication). Outside the WANA region autumn sowing is used in the relatively warm Mediterranean climates of California and Australia. Australia was relatively Ascochyta-free until the mid- 1990s, whereupon chickpea production declined sharply in the Mediterranean, and is recovering only now following the release of more resistant varieties and the adoption of prophylactic management practices (Knights and Siddique, 2002).
While winter temperatures are moderate in Mediterranean Australia (Table 3.2b), autumn sowing exposes chickpea to suboptimal temperatures during flowering
59 Abiotic stresses Biotic stresses Reference
Region Mediterranean rainfall distribution (low–medium PC1 scores), cool climate (low–medium PC2 scores)
Europe: Spain – FW, DRR, AB Cubero et al. (1990)
WANA: Iraq Drought, frost, salinity AB, DRR, BRR, PB, LM, B, W Abbas et al. (1996)
WANA: Turkey Drought, heat, frost AB, LM, PB, B, W Kusmenoglu and Meyveci (1996) North America: USA, Pacifi c North-west – AB, FW, WRR F. Muehlbauer, Washington State
University, 2006 (personal
communication); Acosta-
Gallegos et al. (1990)
South America: Chile Drought, salinity FW, DRR, AB M. Mera, INIA-Carillanca, 2006
(personal communication)
Mediterranean rainfall distribution (low–medium PC1 scores), warm climate (medium–high PC2 scores)
North America: USA, California – AB, FW, WRR F. Muehlbauer, Washington State University, 2006 (personal
communication); Acosta-
Gallegos et al. (1990)
Australia, Mediterranean zone Drought, cold, waterlogging AB, BGM, W Knights and Siddique (2002) WANA: Algeria Drought, heat, cold/frost FW, AB, PB, LM, W Maatougui et al. (1996) WANA: Morocco Drought, heat AB, FW, WRR, LM, B Amine et al. (1996) WANA: Tunisia Drought AB, DRR, LM, PB Haddad et al. (1996) WANA: Syria Drought, heat, frost AB, FW, DRR, PB, LM, W El-Ahmed et al. (1996) WANA: Jordan Drought, frost AB, LM, PB, W Masadeh et al. (1996)
WANA: Israel Heat, drought, cold/frost AB, FW, PB, LM S. Abbo, The Hebrew University of Jerusalem, 2006 (personal
communication)
WANA: Iran Drought, frost, salinity FW, AB, PB, CW, W Sadri and Banai (1996)
WANA: Egypt Heat, salinity, alkalinity WRR, DRR, AB, B, W Johansen et al. (1996); Khattab and El-Sherbeeny (1996) Summer-dominant rainfall (medium–high PC1 scores), cool climate (low–medium PC2 scores)
East Africa: Ethiopia Drought, waterlogging, frost FW, DRR, CR, PB, B Bejiga and Eshete (1996) East Africa Drought, heat FW, DRR, CR, PB, B Bejiga (1990); Saxena (1993) Europe: Poland – FW, WRR, BGM Mazur et al. (2002)
Continued
J.D. Berger and N.C. Turner Abiotic stresses Biotic stresses Reference
Region Mediterranean rainfall distribution (low–medium PC1 scores), cool climate (low–medium PC2 scores)
Australia, summer rainfall zone Drought, cold/frost AB, PRR, BGM, PB, W Knights and Siddique (2002) North America: Canada Late frost–cold, drought AB, FW, WRR T. Warkentin, University of
Saskatchewan, 2006 (personal
communication)
North America: USA, Northern Plains – AB, FW, WRR F. Muehlbauer, Washington State University, 2006 (personal
communication);
Acosta-Gallegos et al. (1990)
South Asia: Nepal Cold, early drought BGM, FW, DRR, PB, B Asthana et al. (1990); Johansen et al. (1996); Pande et al.
(2003); Stevenson et al. (2005)
Summer-dominant rainfall (medium–high PC1 scores), warm climate (medium–high PC2 scores)
North America: Mexico Drought, cold, heat FW, DRR, CR, BGM, PB P. Manjarrez, INIFAP, 2006
(personal communication);
Acosta-Gallegos et al. (1990);
Singh (1993)
East Africa: Sudan Drought, heat FW, DRR, WRR, PB, B, W Faki et al. (1996)
South Asia: Bangladesh Drought, heat, waterlogging BGM, FW, CR, PB, CW Islam et al. (1991); Johansen et al. (1996); Abu Bakr et al. (2002)
South Asia: Myanmar Drought FW, WRR, DRR, PB, Virmani (1996) South Asia: India, northern Drought, heat, cold FW, DRR, AB, BGM, PB, B van Rheenen (1991);
Saxena (1993); Nayyar and
Chander (2004)
South Asia: India, southern Drought, heat, salinity FW, DRR, BGM, PB, B van Rheenen (1991);
Saxena (1993)
FW, Fusarium wilt (Fusarium oxysporum); DRR, dry root rot (Rhizoctonia bataticola); WRR, wet root rot (R. solani); BRR, black root rot (F. solani); AB, ascochyta blight (Ascochyta rabiei); CR, collar rot (Sclerotinium rolfsii); BGM, botrytis grey mould (Botrytis cinerea); PRR, phytophtora root rot (Phytophtora medicaginis);
PB, pod borer (Helicoverpa spp.); LM, leaf miner (Liriomyza cicerina); CW, black cutworm (Agrotis ipsilon); B, bruchids (Callosobruchus spp.); W, weeds.
and can delay podset by more than 30 days (Berger et al., 2004, 2005). Early flowering increases yield stability and specific adaptation to terminal drought, but increases the risk of encountering low temperatures. To optimize chickpea adaptation to Australia, reproductive chilling tolerance is an important breeding priority (Knights and Siddique, 2002).
Spring-sown post-rainy season crop maturing in summer
This is the traditional chickpea-cropping system of Mediterranean climates in WANA and beyond (low–medium PC1 and PC2), which minimizes the risk of winter frosts, chilling and disease stresses, and allows farmers to make planting decisions based on stored soil moisture profiles (Walker, 1996). In general, sowing date is negatively correlated to winter temperature, and the season ranges from February–June in North Africa to May–August/September in the Pacific North-west of the USA (F. Muehlbauer, Washington State University, 2006, personal com- munication) and higher altitudes in Turkey (Kusmenoglu and Meyveci, 1996). As a result, warm regions have relatively longer growing seasons with a shorter aver- age day length (Walker, 1996). Chile is a special case, where chickpea is treated as a bona fide summer crop (August–March), not because of excessively cold winters, but because summer temperatures are relatively low (Table 3.2b), and chickpea production in winter is not as profitable as the other options (M. Mera, INIA-Carillanca, 2006, personal communication). The stress-avoidance strategy is applied differently throughout WANA. For example, in Tunisia winter stresses are minimized by geography, as the crop is grown in low-elevation (<600 m) deep clay loams in semiarid areas, avoiding heavy rainfall (>1000 mm/year), as well as cold and frost-prone areas (Haddad et al., 1996). Conversely, in Turkey, where chickpea is grown across a wide elevation range, time of sowing is used to avoid winter stresses. In central and eastern Anatolia (900–2000 m), where there are 80–120 frosty days/year, chickpea is a summer crop, whereas in western Anatolia, which is much warmer in winter, the season is more typically Mediterranean, run- ning from February to June (Kusmenoglu and Meyveci, 1996).
Although spring sowing in Mediterranean climates avoids the twin stresses of cold and ascochyta blight, it delays crop phenology and increases the expo- sure to terminal drought. This stress severely limits the yield potential of the tra- ditional Mediterranean chickpea-cropping system, and therefore researchers at ICARDA and elsewhere became strong proponents of winter sowing once breed- ing programmes had delivered combined ascochyta blight and cold resistance (Singh, 1990). Subsequent research in Syria and Lebanon has demonstrated that winter sowing can double dry matter production (Hughes et al., 1987) and water use efficiency (Brown et al., 1989), as well as produce taller plants with 70%
(692 kg/ha) more seed yield than the spring-sown crop averaged over 10 years (Singhet al., 1997). Nevertheless, except in Israel, winter sowing has not been widely adopted by farmers in WANA to date, and therefore there is little feed- back on which habitats are most suitable (Walker, 1996). However, it is clear that winter sowing will intensify Ascochyta and frost stresses, and reduce the need for drought tolerance (Walker, 1996). Therefore, high-altitude and cool climate of the Mediterranean represented by low PC2 scores in Fig. 3.2b are expected to be particularly stressful for winter-sown chickpea.
In summer-dominant rainfall regions two different sowing strategies are used for chickpea production depending on temperature. Dryland spring-sown within rainy season cropping is used in cool areas (medium–high PC1, low–medium PC2) such as the Northern Plains in the USA and Canada (F. Muehlbauer, personal com- munication). This region experiences very cold winters (Fig. 3.2b, Table 3.2b). The chickpea season (late April/May–August/September) coincides with the narrow frost-free window suitable for cropping and maximizes the use of the relatively low annual precipitation (Fig. 3.2a, Table 3.2a). Early sowing is preferred, despite delayed germination at soil temperatures of 8–12°C, to prolong the growing sea- son and start flowering early, around the peak of summer in July (Gan et al., 2002).
This cropping system exposes chickpea to considerable Ascochyta risk during the wet, cool spring and low temperatures at the season end, which can delay maturity and damage seeds (McKay et al., 2002). The low temperature finish is considered to be the primary abiotic stress in western Canada, and therefore there is a need for semi-determinate varieties that will mature regardless of soil moisture status (T. Warkentin, University of Saskatchewan, 2006, personal communication).
The autumn-sown post-rainy season cropping system is responsible for the bulk of the world’s chickpea production, and is used throughout the warm sum- mer-dominant rainfall (medium–high PC1 and PC2) regions of South Asia, East Africa, Mexico and north-eastern Australia. Here chickpea is generally grown as a dryland crop on stored soil moisture, on neutral to alkaline fine-textured soils with good water-holding capacity ( Johansen et al., 1996). Extremely low annual rainfall areas such as Sudan (Faki et al., 1996) and north-western Mexico (P. Manjarrez, INIFAP, 2006, personal communication) are exceptions, where chickpea is grown with pre-sowing irrigation, and occasional supplementa- tion within the growing season. In South Asia chickpea sowing is determined by the end of the preceding rainy (kharif ) cropping season, ranging from early October in the south and central India to mid-November in Nepal (Chaurasia, 2001; Berger et al., 2006). Early sowing is preferred to reduce exposure to ter- minal drought (Yadav et al., 1998), but must be balanced against high tempera- ture stress at germination because the temperature gradient is very steep from September to November, particularly in north India. In the south, crop duration is short, typically around 100 days in Hyderabad (Saxena, 1984), and the grow- ing season finishes in late January or early February. Minimum and maximum temperatures vary between 15°C and 30°C, and there is little change after flow- ering commences in December (Berger et al., 2006). Consistent high tempera- tures cause high rates of evapotranspiration, leading to severe terminal drought.
Crop duration in the north is far longer, between 150 and 160 days at Hisar (Saxena, 1984), and the season finishes in March or April. Temperatures in the vegetative phase are 5–10°C lower in the north, but increase very rapidly after flowering in January to early February, ending up with maxima only marginally lower than in the south (Berger et al., 2006). Although podset in the northern regions is often delayed because of low temperatures during flowering (Saxena, 1984), the rapid subsequent temperature increase also imposes considerable terminal drought stress.
In north-eastern Australia chickpea is usually sown in mid-May to limit the exposure to high temperatures after October. The crop can be dry-sown if there
is sufficient stored soil moisture; otherwise farmers wait for an opening rain, which can delay sowing until August in some seasons (E.J. Knights, Tamworth Agricultural Institute, 2006, personal communication). The crop can face high temperature stress at maturity, as average November maxima range from 27°C to 31°C. However, because rainfall tends to increase from October onwards through much of the region, chickpea does not encounter the same terminal degree of drought stress as in South Asian environments.
Chickpea adaptation traits across the habitat range
Given that chickpea is grown in distinctly different habitats characterized by different climates, stresses and cropping systems, it follows that chickpea must have differentiated into distinct ecotypes, reflecting local selection pressures, particularly in those regions where the crop has been grown for millennia (Fig.
3.1). There has been considerable germplasm evaluation over the last 30 years, ranging from resistance screening and characterization of thousands of lines by the international centres (Singh, 1990; Upadhyaya, 2003) to multi-environment tri- als investigating genotype–environment (G × E) interaction in a variety of coun- tries (Berger et al., Chapter 30, this volume), to detailed physiological studies based on small numbers of accessions. However, this research has not paid much attention to germplasm provenance or provided insight into the inter- action between germplasm origin and behaviour in different environments.
Therefore our understanding of chickpea physiology is largely a general one, and does not explain why or how chickpea from different habitats differ. The picture of chickpea emerges as a typical stress-avoiding competitive ruderal (Grime, 1979), in which the major stresses are avoided by a combination of sowing strategies and appropriate phenology. The timing of flowering is deter- mined by additive positive responses to day length and temperature (Roberts et al., 1985). Carbon (C) and nitrogen (N) fixation rates peak immediately prior to podset, and decline rapidly during pod fill (Hooda et al., 1986; Kurdali, 1996), in line with falling leaf water potential and stomatal conductance (Leport et al., 1998, 1999). The bulk of seed N is remobilized from vegetative tissue formed prior to flowering, whereas C mobilization from pre-flowering assimi- lates is low (Hooda et al., 1989, 1990; Kurdali, 1996; Davies et al., 2000). This implies that seeds are filled as rates of photosynthesis decline during pod fill, augmented by recycling of respired C within the pods (Furbank et al., 2004;
Turner et al., 2005). Drought stress speeds up chickpea phenology by decreas- ing the thermal time taken from emergence to flowering, pod fill and maturity (Singh, 1991), and decreases leaf water potential, photosynthesis, pod number and yield (Davies et al., 1999; Leport et al., 2006). The primary adaptive strat- egy to drought stress in chickpea appears to be escape through early phenol- ogy (Silim and Saxena, 1993a,b; Siddique et al., 2001; Berger et al., 2004, 2006). However, chickpea also has a number of characteristics consistent with dehydration postponement and tolerance, such as deep rooting (Saxena et al., 1994), high soil water extraction (Zhang et al., 2000) and osmotic adjustment (Morgan et al., 1991; Lecoeur et al., 1992; Leport et al., 1999; Moinuddin
and Khanna-Chopra, 2004; Basu et al., 2006). Although temperatures >30°C reduce germination, duration of flowering, pod fill, podset, proportion of fer- tile seeds and yield, chickpea is more tolerant of high temperature stress than cool season grain legumes such as faba bean, lentil and field pea (Summerfield et al., 1984; Saxena et al., 1988; van Rheenen et al., 1997; Gan et al., 2004).
Under non-lethal cold stress chickpea delays germination (Auld et al., 1988;
Ganet al., 2002) and podset (Berger et al., 2005) more than well-adapted spe- cies like pea and the annual wild Cicer sp. Similarly, leaf expansion rates are relatively low under cool conditions, and this, combined with small leaf size, means that winter chickpea absorbs less incident radiation (<50% photosyn- thetically available radiation (PAR) ) than other grain legumes, in the early part of the Mediterranean growing season (Mwanamwenge et al., 1997).
To what extent do these characteristics change across different habitats?
There is a paucity of such information in the chickpea literature. Studies on geo- graphical patterns of morphological and agronomic variation in global chickpea germplasm collections have not explained how these traits interact with the environment to play a role in adaptation (Jana and Singh, 1993; Upadhyaya, 2003). Upadhyaya (2003) demonstrated a preponderance of kabuli-type char- acters (white flower and light seed colour, large, smooth-textured seeds) in East Asia, the Mediterranean and Europe, while desi characters (pink flowers, yellow to brown angular seeds with a rough texture) were more common in Africa, and South as well as South-east Asia. These findings reflect the Mediterranean pref- erence for kabuli types, and the predominance of desi types in India and East Africa. Agronomic traits describing phenology, plant architecture and produc- tivity varied widely within regions (Upadhyaya, 2003), which is to be expected given the range of habitats found within any given region (Fig. 3.2).
The best evidence for ecotype formation in chickpea has come from studies that focus on germplasm provenance. Evaluation of a recent C. judaicum collection, in which habitats were described in great detail, demonstrated that this wild species of chickpea is a typical stress-avoider (Ben-David, The Hebrew University of Jerusalem, 2006, personal communication). As habitats become more stressful, in terms of rain- fall (amounts, distribution, variance), temperature (minima, maxima, frost day distri- bution), wind speed, radiation, relative humidity and soil type, reproductive strategies became increasingly conservative, with accessions flowering earlier and accumu- lating less biomass (Ben-David, The Hebrew University of Jerusalem, 2006, per- sonal Communication). G × E studies across Australia and India have demonstrated similar tendencies in chickpea (Berger et al., 2004, 2006). The germplasm with the earliest phenology came from short-season habitats in Gujarat, southern and cen- tral India, followed by northern India and Australia, and finally the Mediterranean.
Germplasm with early phenology was widely adapted throughout Australia (Berger et al., 2004), and was particularly effective in stressful terminal drought environ- ments, such as Merredin in Western Australia, and Sehore, Jabalpur and Gulbarga in central and southern India (Berger et al., 2006). In addition to early phenology, genotypes specifically adapted to low yielding sites in India were characterized by low yield responsiveness, low biomass and high harvest index (Berger et al., 2006).
Conversely, genotypes that were well adapted to higher-yielding northern Indian sites were almost exclusively sourced from Punjab, Haryana, New Delhi and Uttar