More than five foliar diseases caused by Ascochyta blight, chocolate spot, rust, powdery mildew, Cercospora leaf spot, different root rot complexes, nematodes,
Orobanche and a large number of viruses affect the production and productiv- ity of faba bean (Sillero et al., 2010). In North and East Africa, the major biotic stresses are, Ascochyta blight, black root rot, bruchids, chocolate spot and rust (Bayaa, Kabakebji, Khalil, Kabbabeh, & Street, 2004). Other biotic stresses include
Orobanche (Khalil, Kharrat, Malhotra, Saxena, & Erskine, 2004; Maalouf et al., 2011) and different types of viruses, like bean yellow mosaic virus (BYMV), pea enation mosaic virus, bean leaf roll virus (BLRV), FBNYV, true broad bean mosaic virus, broad bean mottle virus, and broad bean stain virus (Bond et al., 1994; Saxena, 1991; van Leur, Kumari, Makkouk, & Rose, 2006). O. crenata can reduce the yield of faba bean in infested areas by up to 90%. The estimated average yield losses due to O. crenata in Morocco ranged from 7% to 80% depending on the level of infes- tation (Gressel et al., 2004). Around 78% of the Moroccan faba bean fields were infested by Orobanche (Mesa-García & García-Torres, 1991). Orobanche-tolerant lines have been developed in faba bean (Khalil & Erskine, 1999; Khalil, Kharrat, et al., 2004; Maalouf et al., 2011). Efforts have been focused on identifying sources of resistance/tolerance to Ascochyta blight, chocolate spot, rust and Orobanche (Bayaa et al., 2004; Hanounik & Roberston, 1989; Khalil, Bayaa, Malhotra, Erskine, & Saxena, 2004; Khalil, Kharrat, et al., 2004; Maalouf, Ahmed, Kabakebji, Kabbabeh, & Street, 2009; Maalouf, Ahmed, Nawar, Khalil, & Bayaa, 2012; Maalouf et al., 2010, 2011), at ICARDA and in other advanced research institutes (Bernier & Conner, 1982; Bond et al., 1994; Rashid & Bernier, 1984, 1986). Among the breeding lines resistant to rust developed at ICARDA are ILB403, ILB411, ILB420, ILB 431, ILB 479, ILB 490, ILB 866, ILB 919, ILB 938, Reina Blanca ILB 249/803/80, ILB 249/804/40, ILB 938, ILB 159-1, ILB 159-4, BPL 710, BPL 1179,
BPL 7, BPL 8, BPL 260, BPL 261, BPL 263, BPL 309, BPL 406, BPL 417, BPL 427, BPL 490, BPL 484, BPL 524,BPL 533, BPL 539, BPL 552, BPL 554, BPL 567, BPL 571, BPL 573, BPL 576, BPL 588, BPL 604, BPL 610, BPL 627, BPL 649, BPL 663, BPL 665, BPL 667, BPL 680, BPL 640, BPL 643 and BPL 702 (Bernier & Conner, 1982; Bond et al., 1994; Khalil, Nassib, & Mohammed, 1985; ICARDA, 1987; Rashid and Bernier, 1984, 1986). As regards pathogenic diversity, several races of U. viciae-fabae have been identified. Using established reference sets (Conner and Bernier, 1982; Emeran, Sillero, & Rubiales, 2001) the highest virulence was identi- fied in the Egyptian populations. The evidence of the physiologic specialization in
U. viciae-fabae described above suggests that the use of single resistance genes in cultivars would not likely result in long-term rust control. So it is a major need to search for strategies to prolong durability. Complete resistance is common (Khalil et al., 1985; Rashid & Bernier, 1984, 1991; Sillero, Moreno, & Rubiales, 2000).
Ascochyta blight is caused by the fungus Ascochyta fabae. It is a common disease that causes yield losses of up to 90% in susceptible cultivars when environmental conditions are favourable for disease development (Hanounik & Roberston, 1989). The fungus infects all the above-ground plant parts including the seeds. Sexual repro- duction allows new virulence combinations and, as a consequence, the pathogen may respond over time to selection exerted by the introduction of host resistance genes. Physiological specialization between pathogen isolates and host genotypes has been described in the A. fabae – faba bean pathosystem (Ali & Bernier, 1985; Avila et al., 2004; Hanounik & Roberston, 1989; Kharbanda & Bernier, 1980; Kohpina, Knight, & Stoddard, 1999; Rashid, Bernier, & Conner, 1991), which is problematic in breed- ing, making it necessary to evaluate segregating breeding materials against a range of isolates to ensure good success. Among the faba bean lines identified as resistant to Ascochyta blight are BPL 74, BPL 460, BPL 471, BPL 472, BPL 646, BPL 818, BPL 2485, ILB 1814, 14434-2, 14434-3, 15025-2, 15035-1, 15041-2, BPL 2485-1, BPL 2485-2, ERF-3-14, BPL 230, BPL 266, BPL 365, BPL 465, ILB 752, L83118, L83120, L83124, L83125, L83127, L83129, L83136, L83142, L83149, L83151, L83155, L83156, L82001, L831818-1, Line 224, ILB 757 Ascot, V-46, V-47, V-165, V-175, V-494, V-1122, V-1220, ILB 1414 and ILB 6561 (Bond et al., 1994; Hanounik & Roberston, 1989; Lawsawadsiri, 1995; Maurin & Tivoli, 1992; Ramsey, Knight, & Paull, 1995; Rashid et al., 1991; Sillero, Avila, Moreno, & Rubiales, 2001).
Chocolate spot is especially severe in humid areas and reported to be the cause of heavy reductions in yields in places, such as Morocco, Tunisia, Egypt, Ethiopia, China, and United Kingdom. The faba bean lines resistant to chocolate spot are BPL 74, BPL 460, BPL 471, BPL 472, BPL 646, BPL 818, BPL 248, 14434-2, 14434-3, 15025-2, 15035-1, 15041-2, BPL 2485-1, BPL 2485-2, BPL 230, BPL 266, BPL 365, BPL 465, ILB 752, L83118, L83120, L83124, L83125, L83127, L83129, L83136, L83142, L83149, L83151, L83155, L83156, L82001, L831818-1, Sel.97Lat.97 132-1, Sel.97Lat.97 132-3 (Bayaa et al., 2004; Kharrat, Le Guen, & Tivoli, 2006). Little is known about the mechanism of resistance to Botrytis. There is a need to establish differential lines and then use these to evaluate the virulence of a collection of isolates of diverse origin, under the same environmental conditions, for the major diseases and broomrapes that attack faba bean.
In addition, more than 180 new sources for resistance to chocolate spot,
Ascochyta blight and rust were identified at ICARDA under heavy soils infested by a mixture of the most virulent pathogens collected in Syria. Lines with combined resistance have been developed at ICARDA and sent to different national agricul- tural research systems to observe the response of the resistant lines to different races in varying environments. In the last 5 years, 70 lines with resistance to chocolate spot and 70 lines with resistance to Botrytis were sent to different national agricul- tural institutes to evaluate their resistance under their specific races and environ- ments. National breeding programs, mainly in Morocco, Sudan and Syria, selected 28 promising lines (Maalouf et al., 2012). In Ethiopia, the major disease problems were chocolate spot, rust and root rots. Several varieties with a high-level resistance to chocolate spot, derived directly or indirectly from the ICARDA breeding pro- gram, were released by EIAR. In addition, because of the high prices of faba bean in Ethiopia, farmers are expanding faba bean production on vertisols that are con- fronted with root rots favoured by stagnant water. Through extensive collaborative research, EIAR researchers have released several high-yielding faba bean varieties through direct selection from the germplasm supplied by ICARDA. Among the faba bean varieties released with good levels of disease resistance are ‘Moti’ (ILB 4432 x Kuse-2-27-33); ‘Gebelcho’ (ILB 4726 x ‘Tesfa’); ‘Obsie’ (ILB 4427 x CS20DK) and ‘Walki’ (ILB 4615 z Bulga 70). The variety ‘Walki’ was developed for water- logged areas and is gaining popularity in the central highlands of Ethiopia. Viruses that infect faba bean crop are not host species-specific; they can affect a range of food and pasture legumes as well as numerous weeds. A ‘green bridge’ between cropping seasons is apparently necessary for the transmission of viruses. The other means of virus survival is seed transmission, which is almost absent or not of eco- nomic importance for faba bean viruses (van Leur et al., 2006). Because of the uncertainty of virus epidemics and the lack of virus control options, growers can perceive viruses as a higher risk than fungal diseases. However, some inbred lines such as 2N23, 2N65, 2N85, 2N101, 2N138, 2N295 and 2N425 were reported in Canada some decades ago as sources of resistance to BYMV, but only one of them, line 2N138, was highly resistant to the necrotic strain of this virus (Gadh & Bernier, 1984). ICARDA has identified different accessions resistant to BLRV (BPL 756, BPL 757, BPL 758, BPL 769, BPL 5278 and BPL 5279), and resistant to BYMV (BPL 1351, BPL 1363, BPL 1366 and BPL 1371) (Bond et al., 1994; Kumari & Makkouk, 2003; Robertson, Singh, Erskine, & Abd El Moneim, 1996).
Efforts to breed faba bean resistant to Orobanche have resulted in the release of cultivars with useful levels of incomplete resistance combined with a degree of toler- ance (Cubero, Moreno, & Hernandez, 1992; Cubero, Pieterse, Khalil, & Sauerborn, 1994; Kharrat, Abbes, & Amri, 2010; Khalil & Erskine, 1999; Khalil, Kharrat, et al., 2004; Maalouf et al., 2011). The resulting resistance, which might be based on a combination of resistance mechanisms, is more likely to last longer than resistance based on a single gene (Perez-de-Luque, Lozano, Moreno, Testillano, & Rubiales, 2007; Rubiales et al., 2006). Little resistance to O. crenata was available in faba bean until the appearance of the Egyptian line F402 (Nassib, Ibrahim, & Khalil, 1982). Some accessions with moderate to low levels of resistance and/or tolerance
have been reported (Table 5.4), but the first significant finding of resistance was the identification of family 402 derived from a 3-year cycle of individual plant selec- tion in an F7 from the cross (Rebaya 40 x F216) made at ICARDA (Cubero et al., 1994). Different cultivars have been developed from this cross (Giza 402, BPL 2210, Baraca, Lines 18009, 18015, 1835, Cairo 241, Cairo 348, Cairo 2, Line 402/294, Lines 402/29/84, 674/154/85, L3-4, Line X-843, Giza 429, Giza 674, Giza 843, ILB 4347, ILB 4357, ILB 4360, Bader, XBJ 90.03-16-1-1-1, Misr1 and Misr2 (Abbes, Kharrat, Delavault, Simier, & Chaibi, 2007; Abdalla & Darwish, 1994, 1996; Cubero et al., 1992; Hanounik, Jellis, & Hussein, 1993; Khalil & Erskine, 1999; Khalil, Kharrat, et al., 2004; Kharrat & Halila, 1994; Nassib et al., 1982; Saber et al., 1999;
ter Borg et al., 1994)).