Abstract: The national uniform wheat and barley yield trial (NUWYT) 2000-2001 comprised of 33 promising candidate lines (29bread wheat, 1 durum wheat and 3 barley). The trial was grouped into three categories viz, rain fed (12 entries), seeding date (18 entries) and barley (3 entries). These promising lines were evaluated at multilocations in different agro-ecological zones against prevalent pathotypes of leaf and stripe rusts. Out of 33 lines, 10 lines were common to NUWYT 1999-2000, of these lines seven lines (NR-149, 95C004, 91BTO10-5, V-97112, SD1200/14, B96038 and B92044) had desirable/acceptable RRI for leaf rust. As these lines have fulfilled two years testing requirement for leaf rust resistant. So these lines can be recommended in those areas where leaf rust problem. Extremely dry weather prevailed throughout the year, so stripe rust could not develop inspite of artificial inoculations.
Introduction
Rusts, viz., Brown or leaf rust (Puccinia recondita Roberge ex Demaz f.sp. tritici (Eriks. E. Henni) D.M. Henderson) and stripe (or yellow) rust (Puccinia striiformis Westend) are by far the most import diseases affecting wheat production in several wheat growing areas of the world (Singh et al., 1998; Mirza et al., 2000; Akhtar et al., 2001). Release of wheat variety is a sensitive issue. For selecting a wheat variety some important characteristics are considered as for any other crop plant such as time of maturity, tolerance to heat stress, disease and insect resistance, shattering and lodging quality and yield. Genetic resistance is the most economical and environmentally safe measure to reduce crop losses. Growing resistant cultivars has no cost to farmers and is the most environmentally safe measure to reduce crop losses. Growing resistant cultivars has no cost to farmers and is the most economical control measure (Singh, 2000 and Line and Qayoum, 1991). Wheat varieties developed through screening survive for 4-5 years under normal environmental condition.
The objectives of this investigations were to evaluate the 33 promising candidate lines (NUWYT 2000-2001) against prevalent pathotypes of stripe and leaf rusts in the country. These lines are the candidate lines developed by the country wheat breeders, tested for yield ability, adaptation and other agronomic characters and rust situation. The wheat varietal evaluation committee (VEC) places a great weightage on the disease resistance of these lines. The rust data form the basis of recommendation by VEC to the provincial and National Seed Council’s (PandNSC) regarding the approval and release of promising high yield rust resistant future varieties. This paper reports the results of NUWYT 2000-2001 evaluated at multilocation throughout the country.
Materials and Methods
The NUWYT trial 2000-2001 comprised of 33 promising candidate lines (29 bread wheat, 1 durum wheat and 3 barley). It was grouped into three categories viz. rain fed (12 entries), seeding date (18 entries), and barley (3 entries). The details of the material in respect of line number, parentage/pedigree and donor institute is given in Table 1.
The trial was planted at 11 locations for leaf rust: 2 in Sindh, 5 in Punjab, 3 in NWFP and 1 in ICT (Islamabad Capital Territory) and 9 locations for stripe rust: 5 in Punjab, 3 in NWFP and 1 in ICT. These locations represent areas comprising different agro-ecological zones and "hot spots", which provide conditions for good development of rusts.
Procedure on planting, rust inoculation, rust observation and calculation of Relative Resistance Index (RRI) was according to NUWYT report 1996-97 (Hussain, 1997).
Artificial rust inoculations with a mixture of field collections supplemented with the inoculum of known virulences of leaf rust were carried out in February 2001 to early April 2001 at CDRI-Karachi, RARI-Bahawalpur, WRI-Faisalabad, NARC-Islamabad, CCRI-Pirsabak, and NIFA-Tarnab. Similarly stripe rust inoculations were arranged in February and March 2001 at NARC-Islamabad, AARI Faisalabad, CCRI-Pirsabak and NIFA-Tarnab. Leaf rust pathotypes possessed virulence for host genes Lr1, 2b, 2c, 3,10,11,14a, 16, 17, 18, 22a, 22b, 23,25,26,30,32,33 and 34. Similarly stripe rust pathotypes possessed virulence to host genes Yr1, 2,6,7,8,9,10,18 and Yr A.
Rust inoculations of the spreaders and checks were carried out by the hypodermic syringe method using aqueous urediospore suspension to which 1 to 2 drops of Tween 20 were added, to break the surface tension. The trials planted at Sahowali (Sialkot), BARI-Chakwal, and NWFP Agriculture University were not artificially inoculated for two reasons: a) that past experience indicated that most of these sites are hot spots for the natural development of wheat rusts and b) that it is desirable to keep the natural parasite population in equilibrium in relations to hosts in these areas.
At all locations, observations on response and severity of stripe and leaf rusts were recorded according to Loegering, (1959). The severity was recorded as percent of rust infection on the plants according to the modified Cobb scale (Peterson et al., 1948). As severity is determined by visual observation, readings cannot be absolutely correct. Therefore, below 5% severity, the intervals used are trace (t) to 2. Usually, 5 percent intervals are used from 5 to 20 percent severity and 10 percent intervals for higher readings.
Readings of severity and reaction are recorded together with severity first.
| TR | = | Trace severity of resistant type infection |
| 10MR | = | 10 percent severity of a moderately resistant type infection |
| 50S | = | 50 percent severity of a susceptible type infection |
The Coefficient of Infection (CI) for both rusts has been calculated in the manner used in CIMMYT and IRN (USDA) (Table 2). Coefficient of Infection was calculated by multiplying the response value with the intensity of infection in percent. Average Coefficient of Infection (ACI) was derived from the sum of CI values of each entry divided by the number of locations.
| Table 1: | List of lines/entries included in National Uniform Wheat Yield Trials 2000-2001 |
| Table 2: | The observation on response of stripe and leaf rusts |
| *According to vast field experience of the Institute in rust research, two new categories have been added. | |
After some modifications a rating scale for disease resistance was adopted by PARC in 1982 for use with cereal rusts (Aslam, 1982), based on scale by Doling (1965) for selecting wheat varieties to powdery mildew and later adopted by ARC of Great Britain for the farmers.
The highest ACI of a candidate line is set at 100 and all other lines are adjusted accordingly. This gives the Country Average Relative Percentage Attack (CARPA). The '0' to '9' scale previously designated as Resistance Index (R.I) has been re-designated as RRI (Relative Resistance Index). From CARPA, RRI is calculated on a 0 to 9 scale, where 0 denote most susceptible and 9 highly resistant.
The RRI is calculated according to the following formula:
The desirable index and acceptable index number for rusts are as below (Aslam, 1982).
| Disease | Desirable Index | Acceptable Index |
| Stripe rust | 7 and above | 5 |
| Leaf rust | 7 and above | 6 or 5 |
Lines which through yield testing show a high degree of yield stability even under high infection conditions, get their Index rating increased by "1".
Results and Discussion
Extremely dry weather prevailed throughout 2000-2001 wheat growing season and in spite of artificial inoculations at most of the sites poor rust development was observed. Stripe rust could not be developed at any of the locations and leaf rust developed only on three locations namely RARI-Bahawalpur, AARI, Faisalabad and CDRI, Karachi.
| Table 3: | Response of candidate lines to leaf rust along with coefficient of infection (C.I.), average coefficient of infection (ACI), country average relative percentage attack (CARPA), relative resistance index (RRI) during 2000-2001 |
| Table 4: | Candidate lines with desireable relative resistance index (RRI) against leaf rusts during 1999-2000 and 2000-2001 |
| Table 5: | Candidate lines with desireable/acceptible relative resistance index (RRI) against leaf rusts during 2000-2001 |
At rest of the locations even susceptible check could not develop a susceptible reaction. Keeping in view this situation leaf rust data recorded at these locations for NUWYT nursery was utilized to calculate ACI, CARPA and RRI which could only be used to assess the resistance of the candidate lines against leaf rust only.
Leaf rust observations were recorded according to Zadoks growth stage 77-85 (Zadoks et al., 1974). As mentioned earlier rust development was satisfactory only at three locations mentioned above and ACIs, CARPA and RRI calculated on the basis of this data is given in Table 3.
Out of 33 lines included in NUWYT 2000-2001, 10 were common to NUWYT 1999-2000. Of these lines only seven lines had desirable/acceptable RRI for leaf rust only (Table 4). These lines include 2 lines from rain fed, 3 from seeding date and 2 from barley. As these lines have fulfilled two year testing requirement for leaf rust resistance only on the three locations, they may be included in the NUWYT 2001-2002 for evaluation against stripe rust at all the locations and against leaf rust at rest of the locations.
In addition to these lines 4 lines from rain fed, 9 from seeding date have also shown acceptable/desirable RRI for the year 2000-2001 at the three locations, which may also be included in NUWYT 2001-2002 for complete analysis (Table 5). The lines possessing Lr27+31, Lr10 and Lr17can be combined with slow rusting type of durable resistance to increase the life of these genes (Mirza et al., 2000). According to unpublished data on virulence analysis, there is no virulence present on resistant gene Lr4, 9,24 when use in combination. In addition to this, the lines with Lr10, 13 and 34 with minor partial resistance genes show durable resistance (Hussain et al.,1999, Ezzahiri and Roelf, 1989; Mc Intosh, 1992; Singh and Gupta; 1991; Singh and Rajaram, 1991). Therefore, the lines having durable resistance genes can safely be released as commercial cultivars in rust prone areas.