Management of Leaf Rust of Wheat through Different Levels of NPK and Sowing Times

Leaf rust (Puccinia triticina f. sp. tritici) is universal threat for wheat production. In present study, effect of sowing dates (30 Oct; 10, 20 and 30 Nov) and NPK levels (N1-80Kg, N2-100Kg, N3-60Kg, P1-58Kg, P2-70Kg, P3-50Kg, K1-63Kg, K2-75, K3-55Kg) against leaf rust and their impact on 1000 grain were evaluated under Randomized Complete Block Design (RCBD) at Plant Pathology research area in University of Agriculture Faisalabad during 2009. Results showed that among 3 fertilizers, K exhibited significant result as compared to N, P and control for management of leaf rust and produced maximum 1000 grain weight. Among sowing dates, rust severity was minimum in early sown (30 Oct) and maximum in late sown (30 Nov). Thus early sowing with different levels of NPK has paramount importance to combat leaf rust severity effectively.


Introduction
Wheat is a vital cereal crop of the 1/3 rd of world's and it is being consumed as staple food [16]. To meet human demands for wheat in 2050, 2% annual increase in wheat production is compulsory on the same cultivated area [56]. It supplies 72% calories and protein in the average diet [10]. In Pakistan, an area of 9,062 thousand hectares is under cultivation with 23,421 thousand tonnes annual production and having 2,585 kg ha -1 average yield. However, the production is highly constrained by rusts which cause losses to wheat are remarkable [31]. Leaf rust (Lr) (Puccinia triticina f.sp. tritici) is globally distributed and the peak disparaging wheat crop foliar disease and wheat production can be jeopardized by this disease especially in favorable conditions [19]. According to Saari [44], leaf rust is cosmopolitan in distribution and is considered an unremitting dilemma. Lr of wheat is a threat in most of wheat growing areas of Pakistan owing to prolonged season for its development and the time of appearance [53]. Lr pathogen is prolific in nature that retains numerous physiological races [24]. These races have different level of virulence and are capable of infecting various wheat cultivars [34]. In Pakistan, several times epidemic form of this disease has appeared [9]. Neglecting the other vagaries which lower the production of wheat, Lr alone can cause 30 to 50 percent yield losses under favorable environment. Rust epidemic history indicates impact of this disease [7]. Yield losses up to 40 to 50% have been recorded in different parts of the world [33]. This loss in yield is influenced by the time of infection and disease intensity [4] or more responsible by the resistance level, and maturity stage of crop when initial infection occurs [28,29]. In case of early onset of rust, grain yield losses in susceptible cultivars may exceed 50% [59].
Sowing time of wheat have prime importance to get maximum yield and manage the leaf rut disease [12] because Puccinia recondite, the causal agent of leaf rust required particular environmental conditions for its survival and spread [26]. Disease resistance in crops is genetically controlled. However, natural disease resistance mechanisms can be enhanced by plant nutrients [35]. Use of balanced fertilizers is a necessary requirement for the best management strategies to increase yield per acre as well as for the control of many plant diseases [51]. Adequate supply of nutrition (NPK) to the crop is reduced the Lr and increased the yield of wheat [11,15].
Keeping in view these above facts, present study was designed to investigate different levels of NPK and sowing times for the management of leaf rust of wheat and their impact on yield.

Effect of Sowing Dates on Leaf Rust and Thousand Grain Weight of Wheat
Universal rust spreader "Morocco" was sown in different sowing dates to optimize date of sowing in response to the rust development. Experiment was conducted at four different sowing dates, early (30 th October), mid (10 th November), late (20 th and 30 th November). Data was recorded on the basis of rust severity, area under Leaf Rust Progress Curve (AULRPC) [47] on each sowing date under natural rust inoculum pressure and its effect on 1000-grain weight was observed.

Evaluation of Different Levels of NPK for Wheat Leaf Rust Management
Different doses of fertilizers (N, P, and K) were applied to find out their effect against leaf rust. Spring wheat cultivar "Morrocco" was planted in 2-4 meters strips. The wheat cultivar (Morocco) was chosen for study because it is highly susceptible to races of Puccinia triticina. Planting was done during moth of October and November 2009. All fertilizers were used at sowing time. Nitrogen in form of urea, Phosphorus in form of triple superphosphate and Potash in form of murate of potash were applied in three replications. These fertilizers were tested at three different doses namely, recommended dose, (N 1 , P 1 , K 1 ), above then recommended (N 2 , P 2 , K 2 ) and below recommended dose (N 3 , P 3 , K 3 ) of each fertilizer (N 1 -80Kg, N 2 -100Kg, N 3 -60Kg, P 1 -58 Kg, P 2 -70Kg, P 3 -50Kg, K 1 -63Kg, K 2 -75, K 3 -55Kg) for an area of one hectare. The "Morrocco" plants were inoculated in the early boot stage. One ml spore suspension (2 X 10 5 urediniospores per ml, 0.02% Tween 20) was injected into the randomly selected plant stems [36]. To ensure the appearance of disease, two sprays of inoculum were also done [48]. Field was irrigated to produce optimum humidity which is necessary for the rust development [14,20]. The plot without any fertilizer application (N o , P o , K o ) in each replication served as a control. Effect of fertilizers (NPK) on Lr severity was recorded by using the modified Cobb's scale [38] and 1000 grain weight was recoded.

Statistical Data Analysis
The trial was laid according to the Randomized Complete Block Design (RCBD). All statistical tests performed using SAS/STAT statistical software [46]. Means were separated using Fisher's protected significant difference (LSD) procedure.

Results
Maximum disease severity was observed on wheat sown on 30 th of November (AULRPC = 623) followed by the wheat sown at 20 th November (AULRPC = 435) and wheat sown on 10 th of November (AULRPC = 345) while minimum was observed on the wheat sown on 30 th October (AULRPC = 218) (Fig. 1). Effect of four sowing dated in response to Lr on thousand grain weight was calculated. Minimum thousand grain weight (34.2) was recorded during late sown at 30 th November, while its value was maximum (37.1) in early sown 30 th October (Fig. 2). Three Nitrogen doses with one control (N 0 -0, N 1 -80Kg, N 2 -100Kg, N 3 -60Kg,) were used against leaf rust in the field trial for testing their effectiveness. All the doses of nitrogen except treatment N 1 statistically increased Lr severity as compared to control. Maximum Lr severity (65) was observed in treatment N 2 followed by N 3 (55) and N 1 (43.33) respectively (Fig. 3). All the doses of nitrogen improved 1000-grain weight over check. Maximum 1000-grain weight (32.60g) was obtained in case of treatment N 1 (Fig. 4). The least effective treatment was proved to be N 2 which gave less weight of 1000-grains (31.60g). In case of phosphorus treatment P 2 expressed maximum reduction in diseases severity (41.66) as compared to P 1 (55), P 3 (46.66) and control (Fig. 5). Maximum yield of 1000-grain weight was obtained in case of P 2 (35.53 g) and P 3 gave (30.83g) (Fig. 6).   Potassium significantly reduced the Lr severity and increased 1000 grain weight compared to control. Maximum reduction in disease severity was observed in treatment K 1 (38.33) and minimum reduction in rust severity was observed in case of K 3 (45.0) (Fig. 7) Maximum yield was obtained in case of treatment K 2 which gave mean 1000-grain weight as 36.50g while the least effective treatment was K 3 gave mean 1000-grain weight as 34.93g (Fig. 8).

Discussion
Wheat is cereal crop of Pakistan and have vital place in Agriculture [54]. For obtaining the highest yield as well as ameliorate the ill the effect of diseases, crop sowing at its ideal time is necessary [39]. In the sowing dates trial, disease severity was maximum (AULRPC = 623) for wheat sown on the 30 th of November while minimum (AULRPC = 435) for wheat sown on the 30 th October. Grain weight was the most affected yield component. Negative correlation was observed between disease severity and 1000 grain weight. Yield losses were maximum for wheat sown on 30 th November (34.2) and minimum for wheat sown on 30 th October (37.1). Yield losses increased with late sowing [17,45] because the temperature (maximum and minimum) and the amount of moisture are the lifesaver for Puccinia recondita on wheat (Triticum aestivum L.). Abnormally high temperatures or inadequate rain may inhibit establishment of volunteer wheat plants after harvest which stops or reduces survival of previous crop P. recondita inoculum [26]. Late sowing (30 th November) of wheat crop decreased the germination count m -2 due to temperature fluctuation which ultimately reduced the 1000 grain weight [45].
Disease resistance in crops is genetically controlled. However, natural disease resistance mechanisms are enhanced by plant nutrients [18]. Use of balanced fertilizers is necessary to increased ha -1 yield and to control plant diseases [1,22,35] because nutrients can interrupt the disease development by disturbing pathogen/ plant physiology [32]. Nutrients level can alter the biochemistry, physiology and especially the cell walls integrity, the host chemical composition and membrane leakage.
Nitrogen is an important fertilizer and is essential for cellular components [23]. High nitrogen dose increased the rust severity. Normally N fertilizers increased plant diseases due to its high use. But nitrogen at recommended (N 1 ) rate (80 kgha -1 ) reduced the disease severity by affecting cellulose formation in plants which ultimately reduce the pathogen multiplication [25] while other treatments (N 2 and N 3 ) increased the leaf rust [21, 43 51, 55] because over dose of nitrogen promote succulent growth and thinner the cell walls making plant more susceptible to diseases. At high /low N rates the metabolism of the plant changes as some key enzymes of phenol metabolism have lower activity, the content of the phenolic decreases and the lignin content may be lower. So, defense system of the plants became weak and disease severity increased [8,57] but all doses of N (N 1 , N 2 , N 3 ) improved 1000-grain weight over check [43].
All the treatments of "Phosphorus" reduced Lr incidence as compared to control but maximum reduction in disease incidence was in case of P 2 because it increased disease resistance by stimulating the defense system of the plants as it plays a vital role in different types of physiological and biochemical processes [27,41,49,60]. All the doses of "Phosphorus" statistically increased 1000-grain weight over check [27,60] but maximum yield was obtained in case of P 2 [2,27]. Appliance of P or K reduced plant diseases directly by different ways; i) by affecting pathogen metabolism, survival and development, ii) by creating hindrance in food supply to pathogen by affecting internal metabolism of the plant, and iii) by disturbing the mode of survival and spread of the pathogen by changing the cell-wall ultra-structures and functions of stomata [37].
Maximum reduction in disease severity was observed in treatment K 1 while minimum in case of K 3 . Our results are in agreement with those of Snyder et al. [50]; Snyder and Mascagni [50] and Sweeney et al. [52]. All the doses of "Potassium" increased 1000-grain weight over check. This result is also in agreement with the findings of Ma et al. [30] who stated that 1000-grain weight progressively increased with the application of K [3, 13].

Conclusions
Sowing dates and different levels of NPK have a critical role in leaf rust management and 1000 grain weight of wheat. Minimum leaf rust severity was recorded on early wheat sown 30 th November.