Diverse responses of old, modern and landraces of Syrian wheat genotypes to common root rot under field conditions

Abstract

The yield response of widely grown cultivars and landraces of Syrian wheat challenged with common root rot (CRR: Cochliobolus sativus) was measured by comparing plots with and without artifi cial inoculation under experimental conditions in two consecutive seasons. The results showed that response to CRR diff ered depending on the susceptibility levels of the wheat cultivars, and that the disease signifi cantly (P<0.05) reduced grain yield, number of tillers and kernel weight. The diseased plants had fewer tillers which consequently reduced grain yield per plant. Yield losses of Triticum durum cultivars were higher than those of Triticum aestivum. In addition, the T. durum landrace Horani exhibited the best level of resistance to the disease, which indicates that this landrace might be a candidate donor for resistance in future breeding programmes. As CRR can dramatically reduce wheat grain yields under favorable conditions, management practices that reduce disease severity are highly recommended. Additional keywords: Cochliobolus sativus, Triticum aestivum, Triticum durum, yield loss. important because reductions in plant biomass are a measure of the combined eff ects of the disease on photosynthesis and other production processes (Fernandez and Conner, 2011). Therefore, this study was carried out to evaluate wheat yield responses to CRR under experimental conditions that are typical of a large part of the wheat-growing areas of western Asia. Materials and Methods Plant material Ten most widely grown cultivars and landraces of Syrian wheat were used in the study. They included two Triticum durum landraces (Horani and Salamoni), four Triticum aestivum cultivars (Bouhouth4, Bouhouth6, Cham2 and Doma4), one T. aestivum introduced cultivar (Maksibak) and three T. durum cultivars (Bouhouth7, Cham3 and Doma1). Seed inoculation Nine isolates of C. sativus, selected on the basis of cultural and morphological characteristics and virulence (Arabi and Jawhar, 2002), were used. These isolates were obtained from subcrown internodes of barIntroduction Common root rot (CRR), caused by Cochliobolus sativus (Ito & Kurib.) Drechsl. ex Dast. [anamorph: Bipolarissorokiniana (Sacc. in Sorok.) Shoem.], is an economically important disease of barley, wheat and other small grains in semi-arid climates worldwide (McKayet al., 2018). CRR causes a brown to black discoloration of the subcrown internodes (SCIs) of wheat (Triticum aestivum L.), which is directly related to yield losses (Mathre et al., 2003; Fernandez Holzgang, 2009). Although fungicides can reduce disease severity, the most eff ective and environmentally sound means of control is through the use of resistant cultivars (Kumar et al., 2002). Wheat interaction with CRR is genotype dependent (Fernandez and Jeff erson, 2004) and aff ected by soil inoculum (Smiley et al., 2005). Therefore, prior to controlling CRR, the potential of this disease to cause losses in wheat growing areas should be evaluated. The impact of CRR on the crop (wheat) is Unauthentifiziert | Heruntergeladen 29.08.19 12:01 UTC © Benaki Phytopathological Institute Arabi et al. 92 ley plants showing CRR symptoms. Each isolate was grown on potato dextrose agar (PDA, DIFCO, Detroit, MI, USA) for 10 days at 22 ±1oC in the dark. After 10-12 days, conidia were collected by fl ooding the plate with 10 mL of sterile distilled water and scraping the colony surface with a glass slide to dislodge the conidia. Equal volumes of conidial suspension of each isolate were mixed and fi ltered through a double layer of cheesecloth. The resulting conidial suspension was adjusted to 5 X 105 conidia/mL. Experimental design The trials were conducted at a site approximately 55 km south of Damascus for two consecutive years (2016-2017), under natural rainfed conditions (350mm annual rainfall). Seed inoculation was performed according to the method described by van Leur (1991), where, 30 g seeds of each cultivar were placed in a plastic Petri dish (12cm in diameter) containing 10 g sterile neutralized peat, 40 ml spore suspension (5 × 105 condia/ml) and 8 drops of natural Arabic gum. Following thorough agitation for 1 min, the seeds were sown at 6 cm depth to promote long subcrown internodes (Kokko et al., 1995) in a randomized complete block design, with three replicate plots (1 m x1 m) separated with a 1-m wide border. Each plot consisted of fi ve rows, 20 cm apart and with 50 seeds per row. Based on laboratory preliminary tests on PDA media, CRR-free seeds were used as controls. Disease evaluation Subcrown internodes (SCIs) were examined 8 weeks post-inoculation by measuring the percentage of SCIs surface showing CRR symptoms using a 0-5 scale, as described by Kokko et al. (1995), where 0 (resistant); 1 = HT (highly tolerant): small light brown lesions covering 1-10% of the SCI; 2 = T (tolerant): light brown lesions covering 11-25% of the SCI; 3 = MS (moderately susceptible): light brown/black lesions covering 26-40% of the SCI; 4 = S (susceptible): black lesions covering 41-75% of the SCI; 5 = HS (highly susceptible): black lesions covering 76-100% of the SCI. 1000-kernel weight (TKW) and yield estimation Three central rows of each replicate plot were harvested at maturity stage to measure grain yield (gr/plant). A 500-seed subsample from each row was used to calculate 1000-kernel weight (TKW). The number of tillers per plant was determined on individual hand-harvested plants. Statistical analysis Data was subjected to analysis of variance using the STAT-ITCF statistical programme (2nd Version). Diff erences between means were evaluated for signifi cance by using Newman-Keuls test at 5% probability level (Anonymous, 1988) Results and Discussion CRR produced brown-dark lesions on SCIs, and these symptoms were more severe on the susceptible cultivar Bouhouth7 (Fig. 1). The results are in agreement with our preFigure 1. Common root rot symptoms (Cochliobolus sativus)on the wheat (a) highly tolerant landrace ‘Horani’ and(b) highly susceptible cv. Bouhouth 7, under fi eld conditions. Unauthentifiziert | Heruntergeladen 29.08.19 12:01 UTC © Benaki Phytopathological Institute Response of Syrian wheat genotypes to common root rot 93 vious observations under natural fi eld conditions (Arabi and Jawhar, 2002). The reactions of the 10 wheat cultivars to C. sativus are presented in Table 1. Signifi cant diff erences (P<0.05) in disease severity were detected among cultivars, with values being consistently higher in the susceptible cultivars, in both years of experimentation. In both seasons, landrace Salamoni was highly susceptible with mean disease severity 83.4 %. The T. durum landrace Horani proved to be the most tolerant having 9.9% disease severity (Table 1). In general, the T. durum cultivars were more tolerant than those of T. aestivum (Table 1). The eff ects of CRR on grain yield are presented in Table 2. During the fi rst growing season (2016), no signifi cant diff erences in yield were observed between plants obtained from inoculated and non-inoculated seeds. During the second growing season (2017), grain yield was reduced by CRR in relation to the non-inoculated seeds in all other cultivars except for the highly tolerant landrace Horani. Moreover, CRR signifi cantly (P<0.05) reduced the TKW of the cvs Bouhouth6 and Maksibak by 18.9 % and 8.6 % in 2016, and by 14.3% and 29.5 % in 2017, respectively (Table 3). The reduction of TKW in the other cultivars diff ered greatly depending on the cultivar (Table 3). As shown in Table 4, the number of tillers decreased signifi cantly (P<0.05) by 28 and 27% in the cvs Bouhouth6 and Cham3, in 2016, and by 37.5 and 39.5%, in 2017, respectively (Table 4). Diseased plants had fewer tillers resulting in reduced grain yield per plant. Similar results were reported by Fernandez et al. (2014) and Duczek and JonesFlory (1993), who found that wheat plants infected by C. sativus early in the season produced fewer tillers than those infected later in the season, which was refl ected in yield per plant. The current study also showed that the average response of wheat cultivars to CRR diff ered with the susceptibility level. These fi ndings are in agreement with those of Rush and Mathieson (1990) and Bhandari and Shrestha (2004). Overall, CRR had a negative eff ect on TKW and the number of tillers produced in susceptible wheat cultivars grown under rainfed conditions in southern Syria. The reduction in total grain yield may be attributed mainly to the reduction in the number of tillers, as reported by Conner et al. (1996). However, according to Fernandez and ConTable 1. Reaction of wheat genotypes to Common root rot (CRR; Cochliobolus sativus) under fi eld conditions in two growing seasons (2016, 2017). Cultivar Origin Severity (% subcrown internodes infected area) Year 2016 Year 2017 Mean eff ect Horani Landrace A11.3dy A8.5d 9.9d Cham3 Syrian (Developed by SGCASR)* A10.3d A9.2d 9.7d Doma4 “ A11.2d B15.9d 13.6d Cham2 “ A15.2d B22.5d 18.9c Doma1 “ A31.2c B17.0d 24.1c Bouhouth4 “ A33.2c B27.9c 30.6c Bouhouth6 “ A42.6ab B48.2ab 45.4ab Maksibak Introduced A66.5ab B58.9b 62.7b Bouhouth7 Syrian (Developed by SGCASR)* A84.9a B77.2a 81.1a Salamoni Landrace A82.97a A84.0a 83.5a Mean A42.11 B36.92 y Means (three replicates/cultivar) preceded by diff erent capital letters (row) and followed by diff erent lowercase letters (column) diff er signifi cantly at P<0.05 according to Newman-Keuls test. *SGCASR: Syrian General Commission of the Agricultural Scientifi c Research. Unauthentifiziert | Heruntergeladen 29.08.19 12:01 UTC © Benaki Phytopathological Institute Arabi et al. 94 ner (2011), CRR directly aff ected the carbon fi xation and other physiological processes in wheat leaves by reducing the upward movement of water and nutrients in plants. CRR had a direct impact on total grain yield of wheat, and therefore, this disease should be considered when managing wheat diseases. Moreover, continued efTable 2. Eff ect o