Physiological responses to water stress and yield of winter wheat cultivars differing in drought tolerance

Moderate to severe drought (water stress) at the reproductive stage is common in the U.S. Southern High Plains (SHP), where wheat is grown as a major winter crop. The objective of this study was to better understand the physiological basis of drought tolerance in elite wheat cultivars. A 2‐yr glasshouse study was conducted using three cultivars (TAM 111, TAM 112 and TAM 304) and two water treatments (wet: adequate water and dry: water‐limited). Overall, TAM 111 and TAM 112 used more water for cumulative evapotranspiration (ET) and had more tillers and greater root mass and shoot mass compared to TAM 304. In the dry treatment, TAM 112 had 67% and 81% more grain yield than TAM 111 and TAM 304, respectively. Water use efficiency for grain (WUEg) and water use efficiency for biomass (WUEbm) were also greater in TAM 112 compared to the other cultivars in the dry treatment. The flag leaves in TAM 112 at mid‐grain filling stage (about 15 days after flowering) had lower stomatal conductance (Gs), intercellular CO₂ concentration (Ci), transpiration rate (Tr) and net photosynthetic rate (Pn), but higher photosynthetic water use efficiency (PWUE) than TAM 111 and TAM 304 under water stress. This study demonstrated a distinct role of gas exchange parameters in response to drought, and TAM 112 was more efficient than TAM 111 and TAM 304 in evolving physiological mechanisms to adapt to water stress.     

International provenance trial of Neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) in the terai region of Nepal

An international provenance trial of Neem (Azadirachta indica A. Juss.) was established in July 1996 at Butwal Research Station of western Terai region of Nepal. It comprised the seed sources of 23 provenances collected from 10 countries including Nepal. A randomized complete block design was used for the experiment with two replications in an area of 1.5 hectares. The objectives of this trail were similar to that of other provenance trials under the International Neem Network. The assessments were made for survival rate, diameter at breast height (DBH), height, crown diameter and straightness of stem at age 5 and age 10. Average survival rates of the provenances in the two assessments were 69.74 and 63.5% respectively. The survival rate ranged from 33% for Kuliyapitiya, Sri Lanka to 92% for Ramannagudu, India. The four provenances Ramannagudu, Sagar, Sunyani, and Lamahi showed ≥80% survival rate. Similarly, Sunyani, Ban Bo, Yezin, Ramannagudu and Doitao showed best performance for DBH. The mean DBH of provenances was 8.74 cm (SD = 2.07). The five provenances namely, Sunyani, Yezin, Ban Bo, Ghaati and Bandia were the best performer for height. The mean height and SD of provenances were 6.29 m and 0.79 respectively. Sunyani had the widest crown diameter at both ages. Ban Nong showed the highest score for the straightness of main stem. Out of the two local provenances of Nepal, Lamahi showed better performance than Geta in many characteristics.     

Interpretation of cloud-climate feedback as produced by 14 atmospheric general circulation models

Understanding the cause of differences among general circulation model projections of carbon dioxide-induced climatic change is a necessary step toward improving the models. An intercomparison of 14 atmospheric general circulation models, for which sea surface temperature perturbations were used as a surrogate climate change, showed that there was a roughly threefold variation in global climate sensitivity. Most of this variation is attributable to differences in the models' depictions of cloud-climate feedback, a result that emphasizes the need for improvements in the treatment of clouds in these models if they are ultimately to be used as climatic predictors.     

Effect of foliar and soil applications of zinc sulphate on zinc uptake,tree size,yield, and fruit quality of mango

To compare the effect of methods (foliar and soil) and rate of application of zinc sulphate on zinc and phosphorus uptake, tree size, yield and fruit quality of mango (Mangifera indica L.) cv. Dusheri, zinc sulphate was applied as a foliar spray application (0.25, 0.50, 1.0%) and soil (0.5, 1.0, 2.0 kg tree^‐1) treatments during the second week of October (during flower bud differentiation period). All the zinc sulphate treatments of soil and foliar spray were effective in increasing the leaf zinc concentrations above recommended adequate level of (>20 mg kg^‐1) whereas control trees maintained low leaf zinc concentrations (13.8 to 13.3 mg kg^‐1). The uptake of foliar‐applied zinc was more rapid than that of soil applied zinc. All the treatments of zinc sulphate except the foliar spray treatment of zinc sulphate (0.25%) significantly increased zinc concentrations in the fruit pulp as compared with those in the control trees. The percent increase in the stem girth of trees was highest with the soil application of zinc sulphate (0.5 kg tree¹) followed by foliar application of zinc sulphate (1.0%) as compared with all other treatments. The percent increase in the tree canopy volume was highest with the foliar application of zinc sulphate (1.0%) followed by soil application of zinc sulphate (1.0 kg tree¹) as compared with control and all other treatments. There was no significant (P<0.05) increase in yield, fruit size and weight, pulp or stone weight with any treatment of zinc sulphate. Total soluble solid (TSS) in the fruit was significantly higher (18.6%) with the treatment of soil application of zinc sulphate (0.5 kg tree¹) as compared with all other treatments of zinc sulphate and the control. Acid and sugar content of the fruit was not significantly affected by the foliar or soil application of zinc sulphate.     

Differential response of cowpea lines to aluminum and phosphorus application

Two pot experiments were conducted, one to evaluate the levels of tolerance of fifteen cowpea [Vigna unguiculata (L.) Walp] lines to aluminum (Al) application, and the second to determine the effect of phosphorus (P) addition on the performance of Al‐tolerant lines (IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐2 77–2) and Al‐sensitive lines (IT 86D‐719, IT 90K‐284–2, and IT 89KD‐349) in an Alfisol with Al amendment. Fourteen of the fifteen lines tested showed decreased root biomass (between 19 to 81% reduction) with Al addition, but this effect was significant for eight of them. Fewer lines showed decreased shoot biomass and grain yield with Al application. Despite little change in nodule number following Al application, there was a significant decrease in nodule weight (between 24 and 53% reduction) for nearly all lines. Phosphorus fertilization increased shoot and root biomass, grain yield, nodule number, and weight, and nitrogen (N) and P content of nearly all lines. Al‐tolerant lines showed higher response in shoot and root biomass and nodulation to P fertilization than Al‐sensitive lines, with the highest response from IT 90K‐277–2. Increase in shoot dry weight as a result of P fertilization was from 64 to 107% for Al‐tolerant lines and from 44 to 48% for the Al‐sensitive lines, and increase in root dry weight was from 46 to 86% for the Al‐tolerant lines and from 7 to 42% for the Al‐sensitive lines. Results of these trials indicated that lines IT 91K‐93–10, IT 93K‐2046–1, and IT 90K‐277–2 have potential for good performance in soil with Al toxicity problems, and that cowpea lines with inherent genetic tolerance to Al will give higher response to P fertilization when grown in soil with Al toxicity problems.     

Genetic mapping and QTL analysis for sugar yield-related traits in sugarcane

Genetic improvement of sugar content in sugarcane would benefit from the availability of sufficient DNA markers and a genetic map. Genetic linkage maps were constructed to identify quantitative trait loci (QTLs) for seedling brix (SB), brix (B), sucrose percent in juice (SUC), stalk number (SN), stalk length (SL), stalk diameter (SD), internodes (INT), number of green leaves (NGL), at three crop cycles across seven environments in a segregating population with 207 individuals derived from a bi-parental cross of sugarcane elite cultivars. Linkage analysis led to the construction of eight linkage groups (LGs) for Co86011 and sixteen LGs for CoH70. The combined length of the two linkage maps was 2606.77 cM distributed over 24 LGs. 31 QTLs were identified: 2 for SB, 7 for B, 6 for SUC, 4 for SN, 1 for SL, 3 for SD, 6 for INT and 2 for NGL at LOD scores ranging from 2.69 to 4.75. 7 QTLs (22 %) had stable effect across crop year and locations. Markers from parents were found to be associated with both positive and negative effect on all of the traits analyzed. The most important QTLs intervals identified in this study using single-dose marker, were qB2, qSUC2, qINT2 and qB2, qSUC2, qSL2, qINT2 located between SSR markers UGSM31₅₄₈ and UGSM31₆₄₉. These QTLs could be put into use in marker assisted breeding.     

Leaf and neck blast resistance reaction in tropical rice lines under green house condition

Rice blast (Magnaporthe oryzae) is the most destructive and epidemic disease of rice. Use of host resistance is the best alternative for disease management. The leaf and neck blast resistance of 182 rice breeding lines were assessed for leaf and neck blast and classified relative to a susceptible check-Masuli and resistant check-Laxmi, from greenhouse experiment in 2005 and 2006. The test plants were inoculated with 10⁵ conidial suspension/ml of M. oryzae at 21 days old seedlings for the leaf blast, and at neck base for the neck blast. Among them, for leaf blast, 77 rice lines were resistant, 43 were moderately resistant, 39 were moderately susceptible and 23 were susceptible. While among the selected 31 rice lines evaluated for neck blast, 4 lines were resistant, 4 were moderately resistant, 16 were moderately susceptible and 7 were susceptible. Leaf and neck infection was significant and positively correlated (r = 0.30, P = 0.05). The rice lines, Barkhe 1032, Barkhe 1034, Barkhe 1035, Barkhe 1036, Barkhe 2014, Barkhe 2024, Barkhe 3019, Super 3004 were resistant to leaf blast and Barkhe 1006, Barkhe 1032, Barkhe 1035, Barkhe 3004 were resistant to neck blast. The rice lines with identification # 11, 69, 137, 168, 182 from Masuli × MT4 parentage, and Barkhe 3017 were susceptible to both leaf and neck blast. Progenies of Irradiated Pusa Basmati (IPB), Kalinga III/IR64 (KIII/IR64), and Masuli/IR64 were resistant to both leaf and neck blast. However, most progenies from Masuli/MT4 showed susceptible reaction to both leaf and neck blast. Thus, rice lines form the IPB, KIII/IR64 and Masuli/IR64 will be promising resistant sources for rice blast in breeding programme.     

Regeneration of mixed conifer forests under group tree selection harvest management in western Bhutan Himalayas

Group selection tree harvest has been proposed as an ecologically sustainable silvicultural technique in mixed conifer forests of the western Bhutan Himalayas. To evaluate this silvicultural technique, we studied the ecological consequences of a group selection tree harvest in mixed conifer forests by assessing 127 circular plots (71 in logged and 56 in unlogged stands) in two forest management units (FMUs). Tree species composition and diversity were similar between logged and unlogged stands. Seedling density and height growth vary by species and were influenced by logging and microsites, with generally taller seedlings found in the logged versus unlogged stands. Early successional shade-intolerant species colonized logged stands. Seedlings growing on bare soil scarified by harvesting had medium vigour while seedlings growing on bryophyte mats showed good vigour in both logged and unlogged stands. Moist sites with a northerly aspect supported profuse conifer seedling regeneration, compared to sites with a dry southerly aspect. Damage to conifer seedlings from herbivore browsing was minimal. Conifer seedling density and height growth was negatively affected by competition from herbaceous vegetation, most notably Salvia officinalis. Group selection tree harvest in southern dry exposures in spruce-dominated stands is silviculturally unsuitable because it alters tree succession.     

Plant invasiveness and target plant density: high densities of native Schima wallichii seedlings reduce negative effects of invasive Ageratina adenophora

Economically feasible strategies to cope with invasive species are urgently needed. Plant density can be increased to reduce competitive effects on target plants. This study indicates that increasing native plant density can be used to reduce the effect of invasive Ageratina adenophora. Seedlings of an indigenous tree species, Schima wallichii, were grown in pots containing uninvaded or invaded soil, with or without A. adenophora leaf litter on the soil surface. Schima wallichii seedlings were also grown at four densities under four levels of A. adenophora leaf litter. Root and shoot biomass and length were measured as response parameters in both bioassays. Schima wallichii growth was inhibited by A. adenophora leaf litter and invaded soil. High litter levels reduced S. wallichii root length and dry weight at low plant densities. The inhibition disappeared at high S. wallichii plant densities. As A. adenophora did not inhibit S. wallichii growth at high plant densities, adjustments of seedling density should be studied as a possible management strategy for invasion by A. adenophora and potentially by other exotic plant species. As density‐dependent growth inhibition is the key characteristic of chemical interference, we propose that phytotoxins contribute to A. adenophora invasion particularly at low densities of native seedlings.