Leaf nutrient status in relation to severity of Ganoderma infection in oil palm seedlings artificially infected with Ganoderma boninense using root inoculation technique

Basal stem rot (BSR) caused by Ganoderma spp., a basidiomycete fungus, is a major devastating disease of oil palm, especially in Malaysia and Indonesia. Several factors were reported to influence the outbreak of BSR disease which include nutrient status, age of palm, types of soil, previous crop and replanting techniques. Elemental nutrient is known to have some beneficial effects on plant disease control. Over many years, macro- and micro-nutrient application has been totally overlooked in oil palm fertiliser programmes in relation to outbreak of BSR disease incidence. A study was conducted to determine leaf nutrient concentrations in relation to severity of Ganoderma infection in oil palm seedlings artificially inoculated with G. boninense using root inoculation technique. This study was conducted at Universiti Putra Malaysia (UPM), Serdang which involved a total of 210 Durax Pisifera (DXP) oil palm seedlings. After inoculation, external and internal symptoms developing on seedlings and disease severity index (DSI, four disease classes of 0, 1, 2 and 3) were recorded. At 15 months of inoculation, leaf samples were collected and macro-nutrient such as Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (Mg) and micro-nutrient such as Copper (Cu), Zinc (Zn), Manganese (Mn), Iron (Fe) and Boron (B) were analysed. Analysis of variance (ANOVA) was performed to test the difference between leaf nutrient concentrations in relation to DSI, followed by comparison means using Least Significant Difference (LSD) test at 0.05 significant levels. A total of 25.0% of inoculated seedlings were dead due to G. boninense infection. Significant difference of leaf nutrient concentration in relation to DSI was observed. Leaf macro-nutrient concentration of N, K, and Ca showed significant difference (p<0.05) while P and Mg showed no significant difference in relation to BSR disease development. Meanwhile, leaf micro-nutrient concentration of Cu, Mn and B showed significant difference (p<0.05) while Zn and Fe showed no significant difference. Among significant nutrients, Ca and Cu were found higher in healthy seedlings (DSI - 0) compared to infected seedlings (DSI – 1, 2 or 3). This study suggested that formulation of fertiliser consists mainly of Ca and Cu are needed in order to reduce BSR disease incidence in oil palms

Characterisation and pathological variability of Exserohilum turcicum responsible for causing corn northern leaf blight (BCLB) disease in Malaysia

Aims:Corn is grown primarily for human consumption. It is considered as the second most important cereal crop after rice in Asia. Many diseases affect this crop due to planting of susceptible hybrids. This research is aimed to characterize the causative agent of northern corn leaf blight disease in Malaysia, caused by Exserohilum turcicum.Methodology and results: Leaf samples were collected from infected farms of 2 corn growing areas of Peninsular Malaysia in 2015. A total of 5 fungal isolates were examined for cultural, morphological and molecular properties, and based on the results, the five isolates were identified asE. turcicum. The conidial shapes were observed to be elongated and spindle. Cultural characteristics showed that variation existed among the isolates in colony growth and colour. Mycelia growth rates of the isolates were significantly different on potato dextrose agar (PDA),corn meal agar(CMA)and potato sucrose agar (PSA)media, growth on CMA was faster than on PSA and PDA. The isolates were grouped into three groups based on colony colour i.e. light gray, gray and dark gray. The isolates were categorized into 2 groups based on growth namely, moderate growth and profused growth. The number of septa ranged from 5-7 to 7-10 representing isolates ET002 and ET003, respectively. Similarly, conidial length varied from 56.7 μm to 89.44 μm for isolates ET002 and ET003, respectively. The pathogenic variability tested on Thai Super Sweet (TSS) corn variety, showed that isolates ET001 and ET003 were more aggressive while isolate ET005 was less aggressive among the isolates tested.Conclusion, significance and impact of the study:Both morphology and molecular results showed that, the isolates were identified as E. turcicum. The findings of this study will serve as a baseline for future studies and will help to minimize losses in yield

Characterisation and pathological variability of Exserohilum turcicum responsible for causing northern corn leaf blight (NCLB) disease in Malaysia

Aims: Corn is grown primarily for human consumption. It is considered as the second most important cereal crop after rice in Asia. Many diseases affect this crop due to planting of susceptible hybrids. This research is aimed to characterize the causative agent of northern corn leaf blight disease in Malaysia, caused by Exserohilum turcicum. Methodology and results: Leaf samples were collected from infected farms of 2 corn growing areas of Peninsular Malaysia in 2015. A total of 5 fungal isolates were examined for cultural, morphological and molecular properties, and based on the results, the five isolates were identified as E. turcicum. The conidial shapes were observed to be elongated and spindle. Cultural characteristics showed that variation existed among the isolates in colony growth and colour. Mycelia growth rates of the isolates were significantly different on potato dextrose agar (PDA), corn meal agar (CMA) and potato sucrose agar (PSA) media, growth on CMA was faster than on PSA and PDA. The isolates were grouped into three groups based on colony colour i.e. light gray, gray and dark gray. The isolates were categorized into 2 groups based on growth namely, moderate growth and profused growth. The number of septa ranged from 5-7 to 7-10 representing isolates ET002 and ET003, respectively. Similarly, conidial length varied from 56.7 μm to 89.44 μm for isolates ET002 and ET003, respectively. The pathogenic variability tested on Thai Super Sweet (TSS) corn variety, showed that isolates ET001 and ET003 were more aggressive while isolate ET005 was less aggressive among the isolates tested. Conclusion, significance and impact of the study: Both morphology and molecular results showed that, the isolates were identified as E. turcicum. The findings of this study will serve as a baseline for future studies and will help to minimize losses in yield

Efficient callus induction and plant regeneration of Malaysian indica rice MR219 using anther culture

Rice plant regeneration via anther culture possess several difficulties, these included early anther necrosis and high albinism frequency. In the present study, several biotic and abiotic factors were studied to develop an efficient protocol for the regeneration of Malaysian indica rice MR 219 variety. Callus initiation of anther cultures was evaluated using different N6 media supplemented with 2,4-D in combination with 1-naphthaleneacetic acid (NAA), kinetin (Kin) or 6-benzylaminopurine (BAP). The present study revealed that incorporation of 1.0 mg/L of 2,4-dichlorophenoxyacetic acid (2,4-D) with 3.0 mg/L of NAA significantly elevated callus induction rate with 8.45%. Callus development was further enhanced with the application of 1.0 mg/L of 2,4-D in combination with 1.0 mg/L of BAP, which resulted in 80.83% of globular callus formation rate. Formation of rooty callus (70.83%) was initiated by 0.5 mg/L of 2,4-D in conjunction with 0.5 mg/L of BAP treatment. The highest somatic embryogenesis rate (25.83%) and regeneration frequency (10.92%) was achieved under 4 °C during 7th day, together with the formation of 2.17 green rice plantlets. Nevertheless, culture browning frequency increased over time and reached the highest (100.00%) at 29th day for both 4 and 8 °C treatments. The highest number of albino plantlets was recorded at 18.17 for in vitro cultures maintained under 8 °C at 14th day. The study herein developed an efficient protocol which enhanced callus development as well as the regeneration of green indica rice plantlets while minimizing albinism

Disease resistance of improved MR220 lines against Pyricularia oryzae Cavara and their preliminary agronomic performance

Blast disease caused by Pyricularia oryzae is one of the most destructive fungal diseases of rice in Malaysia. Utilisation of resistant varieties is the most efficient management approach towards reducing yield losses. The line IRTP21683 with the Pi9 gene has shown strong resistance against the isolate MPO988.3 of pathotype P0.0, the most prevalent P. oryzae pathotype in Malaysia. Crossing of IRTP21683 was undertaken with the recurrent parent MR220, a susceptible elite Malaysian rice variety, using a marker assisted backcrossing technique with two simple sequence repeat markers, RM19776 and RM7311, as the tag for the Pi9 gene. Twenty BC3F4 lines with the Pi9 gene were resistant when challenged with MPO 988.3. The cluster analysis based on seven agronomic parameters showed that the resistant BC3F4 lines could be divided into four groups, of which the members in group 1 and 2 have shown comparable or better performance than MR220. Five lines in group 1, B220PI9-3-48, B220PI9-3-76, B220PI9-3-77, B220PI9-3-79 and B220PI9-3-82 showed outstanding yield performance with early maturation

Establishment of effective plantlets regeneration protocol via isolated microspore culture in Malaysian indica rice MR219

The current study recognised the issues encountered in regenerating Malaysia MR219 rice plantlet via microspore culture and attempted to develop an efficient protocol in overcoming the restraints. In the present study, a high proportion of uninucleate microspores (49.17%) was isolated from Stage 2-Segment II panicle (59–61 days), which also exhibited the highest callus initiation rate of 8.50%. Maintenance of the panicles under a cool temperature of 4 °C for 7 days before isolating the microspores, resulted in the highest microspore viability of 58.33% and callus initiation rate of 9.33%. The microspore isolation protocol was also optimised in the present study. The filtration sieve engagement with a pore size of 80 µm and further suspension centrifugation at 800 rpm for 5 min produced the highest microspore viability percentage and callus initiation rate. The incorporation of 3.0 mg/L kinetin in conjunction with 0.5 mg/L 2,4-D greatly enhanced the callus initiation rate, with 11.33%. The callus proliferation capacity, with the formation of 481.67 mg callus, was significantly promoted by the addition of 1.0 mg/L kinetin and 0.5 mg/L 2,4-D into the growth medium. Moreover, a higher green plantlet regeneration frequency of 2.83% was induced by the supplementation of 8% sucrose, which produced an average of 3.50 green plantlets

Overexpression of type II rice metacaspase, OsMC4, increases endoplasmic reticulum stress tolerance in transgenic rice calli

The endoplasmic reticulum (ER) is an organelle responsible for regulating protein synthesis in plants. High salinity can lead to the accumulation of misfolded proteins, resulting in an ER stress response mechanism known as the unfolded protein response (UPR). Failure of the UPR to reverse the effect of protein misfolding will activate programmed cell death (PCD). Metacaspase genes are known regulate PCD in plants. This study aims to provide a comprehensive analysis of the expression patterns of type II rice metacaspase (OsMC) genes in response to ER and salinity stress in rice leaf. Among five type II metacaspases in the rice genome, OsMC4, OsMC5, and OsMC8 expressions were found to be upregulated during treatment with tunicamycin (ER stress) and sodium chloride, NaCl (salinity stress). A construct of taqRFP::OsMC4, controlled by the CaMV35S promoter, was generated and transformed into rice calli. The transgenic rice calli overexpressing taqRFP::OsMC4 demonstrated significant changes in the expression of the ER stress-marker genes, protein disulfide isomerase (OsPDI), and binding immunoglobulin protein (OsBiP). The results from this analysis provide preliminary evidence that at least one of the type II metacaspases, OsMC4, is be able to reduce ER and salinity stresses in rice. Further functional analysis of OsMC genes in ER and salinity stress tolerance could be carried out in transgenic rice overexpressing OsMCs in the future to improve stress tolerance. Simple summary: Oryza sativa, commonly known as rice, is one of the most consumed crops in the world. In response to multiple biotic and abiotic factors, a series of endoplasmic reticulum (ER) stress response regulators are activated. There is evidence that high salinity triggers ER stress in plants. This study aims to determine the level of gene expression among type II metacaspases in rice in response to ER and salinity stress and to assess how they may be linked to PCD in rice calli. Three metacaspase genes, OsMC4, OsMC5, and OsMC8, have been observed to have significant expression post-treatment with tunicamycin in rice leaf. Overexpression of taqRFP::OsMC4 in rice calli significantly reduces the expression level of the stress markers, OsBiP and OsPDI, indicating that the stress level is relatively lower in the transgenic calli compared to the wild-type calli. Therefore, overexpression of taqRFP::OsMC4 in rice may increase rice tolerance towards ER and salinity stress. These expression analyses of the OsMCs family provide valuable information for further functional studies on the biological roles of OsMCs in ER and salinity stress responses.</p