Transcriptomics analysis of phloem-feeding insect resistance in rice germplasm

The Brown Plant Hopper (BPH) is a serious pest of rice in Asia. Development of novel control strategies can be facilitated by a comparison of BPH feeding behaviour on varieties exhibiting natural genetic variation, and then an elucidation of the underlying mechanisms of resistance. We began by understanding BPH feeding behaviour on 12 rice varieties with different resistance background using Electrical Penetration Graph (EPG) and honeydew clock experiments. Seven feeding behaviours (waveforms) were identified and could be classified into two phases, feeding and non- feeding. Cluster analysis has separated the 12 varieties into 3 main groups, resistant, moderate and susceptible. Then, we undertook microarray analysis on all varieties to identify candidate genes which may contribute to resistance. The results reveal the difference between resistant and susceptible varieties. The data agree with EPG and honeydew clock experiments. A total of 21556 probes passed filter in statistical analysis using quantile method (in Genespring) and 239 probes significantly contributed to the difference between resistant versus susceptible (Volcano analysis). Some of them were found to be highly correlated with EPG data and could therefore be potential resistance candidate genes against BPH such as gene encoding hexose transporter, protein kinases, Alpha-DOX2 and peroxidase

Kepelbagaian dan Pewarisan Genetik Sifat Kandungan Pemakanan Ubi Keledek (Ipomoea Batatas (L) Lam.)

Kandungan pemakanan sebanyak 198 aksesi keledek dari Semenanjung Malaysia, Sabah, Sarawak dan AVRDC telah diana lisa menggunakan NIRS. Semua sifat pemakanan yang dikaji menunjukkan nilai CV melebihi 20 % kecuali kanji (6.7%) dan berat kering (12.1%). Nilai purata bagi semua kandungan pemakanan adalah hampir sama dengan nilai yang pernah dilaporkan oleh para penyelidik seluruh dunia ia itu 21.9% (berat kering), 74.8% (kanji), 3.5% (protein), 14.4% (gula), 3.1% (gentian) dan 1.4% (abu). Kajian juga menunjukkan aksesi keledek dari Kel antan dan Terengganu mempunyai nilai kandungan pemakanan yang harnpir sarna dari segi purata dan julat kandungan pernakanan. Kernungkinan ia terdiri dari keledek yang sama. Analisis peminimum varian Ward telah memisahkan 198 aksesi keledek tersebut kepada 5 kumpulan. Kumpulan 2 adalah kumpulan terbanyak yang mengandungi 112 aksesi dan menunjukkan nilai kandungan pemakanan yang sederhana. Kumpulan 5 pula adalah kumpulan terkecil yang hanya mengandungi 6 aksesi sahaja. la mempunyai kandungan kanji yang melebihi 85%. Kumpulan 4 pula adalah kumpulan yang mempunyai nilai kandungan pemakanan yang terbaik. Sementara kumpulan 3 mempunyai nilai kandungan pemakanan yang paling rendah. Keputusan analisis ini menunjukkan kebanyakan varieti keledek yang ditanam oleh petani amnya di Malaysia mempunyai kualiti pemakanan yang agak rendah. Ini menunjukkan sifat pemakanan tidak diberi perhatian oleh petani dalam pemilihan varieti yang akan ditanam

Effects of pre-anthesis drought stress on yield components and seed quality of rice (Oryza sativa L.)

Sufficient supply of high quality planting materials is vital for a successful rice production. Pre-anthesis drought stress significantly reduces yield components of the lowland cultivated rice hence scientific information on its effect on seed quality is still very much lacking. This study was conducted to compare the effects of pre-anthesis drought stress on yield components and seed quality of two rice genotypes, a drought tolerant Moroberekan (V1), and local drought susceptible MR297 (V2). Three durations of drought stress used in this study were well-watered condition (S1), five days stress duration (S2), and ten days stress duration (S3). Complete (100%) spikelet sterility was observed for MR297 as compared with Moroberekan (31%) under S3. The seed germination rate of Moroberekan was significantly lower (p<0.05) under S1 (48%) as compared with S2 (80%) and S3 (70%). However, embryo of the non-germinated seeds of Moroberekan were still alive based on tetrazolium test thus indicated that the seeds were still viable yet dormant. In contrast, seed germination rate of MR297 was not affected by pre-anthesis drought stress (88% for S1 compared to 93% for S2). Therefore, seeds of MR297 produced under pre-anthesis drought stressed condition could be safely distributed in rice seeds supply chain

Response of primed rice (Oryza sativa L.) seeds towards reproductive stage drought stress

Seed priming could be promoted as a potential alternative in alleviating drought stress challenges in rice cultivation. The present study was conducted as an attempt to verify potential performance of seed priming in improving seedling growth and harvestable grain yield of rice under reproductive stage drought stress (RS). Seed treatments involved were non-primed seeds as control (T1), hydro-primed (T2) and osmo-primed at -1.0 mPa with polyethylene glycol (PEG6000) (T3). Reproductive stage drought stress (RS) was imposed at soil water potential lower than -60 kPa. The well-watered plants served as control of the experiment. In general, seedling growth of T3 was better than T2 and T1 for all growth parameters in both planting seasons. Yield components were significantly lower in RS as compared to well-watered treatment (WW). The agronomic performance of primed seeds in T2 and T3 were not significantly different with T1 under both RS and WW for both planting seasons. As a conclusion, seed priming treatments used in this study was ineffective in improving agronomic performance of rice under RS. Therefore, other alternatives such as development of drought tolerant rice should be highly emphasized in order to minimize the impact of drought on growth and yield of rice plant

Drought-induced changes in the flowering capacity, anthesis quality and seed set in rice (Oryza sativa L.)

Drought stress significantly reduces grain yield (GY) due to poor spikelet fertility and anthesis quality. Aim of this study was to understand the changes of flowering capacity, anthesis quality traits and seed set in the re-watered drought stressed modern high yielding drought susceptible rice cultivar, IR64 at heading (DSH) and booting (DSB) stages. The wellwatered plants served as control of the experiment. Results obtained suggest that spikelet moisture content at above 80% was required to maintain optimum anthesis process in rice. Anthesis process in DSH plant was suspended when leaf relative water content (LRWC) dropped to below than 70%. Effects of drought stress on the spikelet moisture were irreversible as compared to the leaf rolling and LRWC. Hence, seed set was failed to occur at the upper rachis branches of the DSH plant. Anthesis process in the re-watered drought stress plants was resumed on the third day after re-watering with about 50% and 80% of anthers managed to dehisce in the DSH and DSB plants. Consequently, percentage of spikelet fertility and seed set in the DSH and DSB plants were increased towards the lower parts of the panicle. The GY, number of seeds, spikelet fertility, and harvest index however were significantly lower in the DSH plant (0.30 g, 13, 16.40%, and 14.81) as compared to DSB plant (1.34 g, 57, 59.14%, and 48.30), respectively. In addition, all interrelated traits involved in the flowering process of rice could be collectively termed as the anthesis quality traits due to their significant correlation with the grain yield and other yield components

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

Brown Planthopper (N. lugens Stal) Feeding Behaviour on Rice Germplasm as an Indicator of Resistance

BACKGROUND: The brown planthopper (BPH) Nilaparvata lugens (Stal) is a serious pest of rice in Asia. Development of novel control strategies can be facilitated by comparison of BPH feeding behaviour on varieties exhibiting natural genetic variation, and then elucidation of the underlying mechanisms of resistance. METHODOLOGY/PRINCIPAL FINDINGS: BPH feeding behaviour was compared on 12 rice varieties over a 12 h period using the electrical penetration graph (EPG) and honeydew clocks. Seven feeding behaviours (waveforms) were identified and could be classified into two phases. The first phase involved patterns of sieve element location including non penetration (NP), pathway (N1+N2+N3), xylem (N5) [21] and two new feeding waveforms, derailed stylet mechanics (N6) and cell penetration (N7). The second feeding phase consisted of salivation into the sieve element (N4-a) and sieve element sap ingestion (N4-b). Production of honeydew drops correlated with N4-b waveform patterns providing independent confirmation of this feeding behaviour. CONCLUSIONS/SIGNIFICANCE: Overall variation in feeding behaviour was highly correlated with previously published field resistance or susceptibility of the different rice varieties: BPH produced lower numbers of honeydew drops and had a shorter period of phloem feeding on resistant rice varieties, but there was no significant difference in the time to the first salivation (N4-b). These qualitative differences in behaviour suggest that resistance is caused by differences in sustained phloem ingestion, not by phloem location. Cluster analysis of the feeding and honeydew data split the 12 rice varieties into three groups: susceptible, moderately resistant and highly resistant. The screening methods that we have described uncover novel aspects of the resistance mechanism (or mechanisms) of rice to BPH and will in combination with molecular approaches allow identification and development of new control strategies

Comparison percentage of time for different EPG waveform feeding patterns of <i>N. lugens</i> on different rice varieties for 5 h (8-12 h). (Average percentage frequency and standard error).

<p>Means± SE within columns followed by the same letters are not significantly different (P<i>></i>0.05, Kruskal- Wallis and Duncan test).</p><p>** =  Significant at 1% probability level; ns  =  Non-significant.</p

Honeydew production over 12 h by <i>N. lugens</i> on 12 rice varieties using the honeydew clock method.

<p>Means± SE within columns followed by the same letters are not significantly different (P<i>></i>0.05, Duncan test).</p><p>** =  Significant at 1% probability level; *  =  Significant at 5% probability level; ns  =  Non-significant.</p><p>‘-‘  =  no honeydew observed in 12 h.</p