Origin Common wheat. Pathogenic Variability Not known.
Reference Stocks
s: Cappelle Desprez and substitution line Cappelle Desprez/Mara 2D differ in the presence and absence, respectively, of Yr16.
PLATE 4-16. Yr16
Adult leaves of Cappelle Desprez and chromosome substitution lines; infected with IPSR pt. 104 E137 (Type 1) (L to R): Capelle Desprez (CD), CD/Bezostaya 2D, CD/Desprez 80 2D, CD/Mara 2D, CD/Poros 2D and CD/Vilmorin 27 2D. The substitution lines from various chromosome 2D sources in CD resulted in a range of disease responses indicating further genetic variation among the substituted 2D chromosomes. Courtesy R Johnson.
Source Stocks
The distribution of Yr16 is difficult to ascertain in the absence of contrasting pathotypes or appropriate genetic studies.
Use in Agriculture
Yr16 presumably contributes to the oligogenic resistance and possibly to the durable stripe rust resistance of
Cappelle Desprez.
Yr17
(Bariana and McIntosh, 1993) (Plate 4-17)Chromosome Locution
2AS (Bariana and McIntosh, 1993). In wheat Lr37 is closely linked in coupling with Sr38 and Yr17, and in repulsion with Lr17 (Bariana and McIntosh, 1993).
Low Infection Type ; C to; 1. Environmental Variability
Moderate, seedlings with Yr17 become more susceptible at lower temperatures and at low light intensities (Bariana, 1991; Bariana and McIntosh, 1994).
Origin
T. ventricosum. Resistance was transferred to the hexaploid wheat line VPM1 (T. ventricosum/ T. turgidum var.
persicum//3*T. aestivum cv. Marne) by Dr G Doussinault and colleagues in France (see Doussinault et al., 1988). Although the primary aim was to transfer eyespot resistance to bread wheat, resistance to rust diseases was also achieved.
Pathogenic Variability
Most isolates of P. striiformis f. sp. tritici are avirulent on seedlings of VPM1. Virulence on cvv. Hyak and Madsen was found in the USA (Line et al., 1992).
Reference Stocks
i: Avocet S*6/VPM1; Kulin*5/VPM1; Spear*5/VPM1. Bindawarra*4/VPM1 Yr6. Thatcher*8/VPM1, R.L.6081
Yr7 (Bariana and McIntosh, 1993).
v: Hyak (Allan et al., 1990); Madsen (Allan et al., 1991); Rendezvous (Bariana and McIntosh, 1993); Sunbri (Brown et al., 1991); VPM1 (Bariana and McIntosh, 1993).
Source Stocks
Cv. Trident;
Australian backcross derivatives additional to those listed above.
B A
PLATE 4-17. Yr17
Seedling leaves of (L to R): A. VPM1, Rendezvous, Spear*4/VPM1, Spear, Cook*3/VPM1 and Cook, and B. VPM1, Rendezvous, VPM1*4/Hartog, Hartog, Thatcher*8/VPM1 and Thatcher; infected with pt. 110 E143 A+. The expression of resistance conferred by Yr17 is significantly influenced by genetic background (see Thatcher, for example) and by temperature and light (Bariana, 1991; Bariana and McIntosh, 1994).
Use in Agriculture
Although interest in VPM1 was primarily directed at the eyespot, (caused by Pseudocercosporella herpotrichoides) resistance located in chromosome 7D, additional selection by both European and USA breeders resulted in rust resistance. In Australia, selection was only for rust resistance.
Tr18 (Singh, 1992a) (Plate 4-18)
Adult plant resistance
Chromosome Location
7D, probably 7DL (see Lr34). Yr18 is possibly completely linked with Lr34 (McIntosh, 1992a; Singh, 1992a) and also with Ltn which controls a distinctive leaf tip necrosis (Dyck, 1991; Singh, 1992b).
Low Infection Type
Mature plants of wheats with this gene are distinctly more resistant than closely related counterparts not possessing it. The infection type is 'resistant' with up to 20% flag leaf area affected by symptoms.
Environmental Variability
Singh (1992a) mentioned that wheats with Yr18 displayed inadequate resistance in some locations in Ecuador and Kenya.
Origin
Common wheat. The history of Yr18 presumably is identical to that of Lr34. Many pedigrees trace back to South American wheats, but a Chinese origin is possible (Dyck, 1991). It is of interest that the development of Frontana in South America followed a damaging stripe rust epidemic in the early 1940s.
Pathogenic Variability Not known. B A D C
175
PLATE 4-18. Yr18
A. Flag leaves of field-grown plants of Thatcher and derivatives; infected with stripe rust and leaf rust. (L to R): R.L.6050, R.L.6058, Line 896 and Thatcher. The first three lines were generated in Canada by selection only for resistance to leaf rust: R.L.6050 and R.L.6058 carry Lr34, but Line 896 does not. Significant levels of both stripe rust and leaf rust are evident on the last two lines.
B. Flag leaves from field-grown plants at Toluca, Mexico, showing leaf tip necrosis (first three leaves) which is associated with the presence of Lr34 and Yr18. The fourth leaf is from a cultivar not possessing these genes and is unaffected by necrosis. Courtesy RP Singh.
C. and D. Adjacent hill plots of Jupeteco 73R and Jupeteco 73S, at Toluca, Mexico. Most of the visible disease symptoms on both wheats were caused by stripe rust although both stripe rust and leaf rust were present in the nursery. The presence of
Yr18 In Jupeteco 73R reduced the leaf area affected from almost 100% to about 20%. Courtesy RP Singh.
Reference Stocks
i: Thatcher lines with Lr34 (see Lr34) (McIntosh, 1992a; Singh, 1992a). The selections, Jupeteco 73R and Jupeteco 73S (Singh, 1992a) can be considered a near-isogenic pair.
Source Stocks
Wheats with Lr34 (see Lr34).
Use in Agriculture
Yr18
hasbeenwidelydeployedinspringwheatsandatleastsomewinterwheatseitherbyits association withleaf rust resistance or by its phenotypic effect on stripe rust response. Anza = WW15 = Karamu = T4, considered to have durable stripe rust resistance (see Singh, 1992a), was widely used in wheat breeding in Australia and at least some of its derivatives, such as Condor, apparently carry Yr18 (Singh, 1992a). Selections of another derivative, Avocet, possess no adult plant resistance and have been adopted as susceptible standards for genetic studies in Australia where they repeatedly display responses of 100S in the field. The original cultivar, Avocet, was heterogeneous for the seedling resistance tentatively designated YrA (probably complementary genes, Wellings et al., 1988) and also for adult plant response to pathotypes virulent on seedlings with YrA.