Piyada Tantasawat

Defensive role of tomato polyphenol oxidases against cotton bollworm (Helicoverpa armigera) and beet armyworm (Spodoptera exigua).

Tomato (Solanum lycopersicum) polyphenol oxidases (PPOs), enzymes that oxidize phenolics to quinones, have been implicated in plant resistance to insects. The role of PPO in resistance to cotton bollworm [Helicoverpa armigera (Hübner)] and beet armyworm [Spodoptera exigua (Hübner)] (Lepidoptera: Noctuidae) was evaluated. Consumption, weight gains, and mortality of larvae feeding on foliage of transgenic tomato lines overexpressing PPO (OP lines) and of larvae feeding on foliage of transgenic tomato lines with suppressed PPO (SP lines) were compared with consumption, weight gains, and mortality of larvae feeding on non-transformed (NT) plants. Increases in foliage consumption and weight gains were observed for cotton bollworms feeding on leaves of SP plants compared to NT and OP plants. PPO activity was negatively correlated with both weight gains and foliar consumption of cotton bollworm, substantiating the defensive role of PPO against this insect. Similarly, beet armyworm consumed less foliage (both young and old leaves) from OP plants than SP plants. Larvae feeding on OP leaves generally exhibited lower weight gains than those feeding on SP leaves. These results indicate that tomato PPO plays a role in resistance to both cotton bollworm and beet armyworm.

Association of RGA-SSCP markers with resistance to downy mildew and anthracnose in grapevines.

Downy mildew (Plasmopara viticola) and anthracnose (Sphaceloma ampelinum) are two major diseases that severely affect most grapevine (Vitis vinifera) cultivars grown commercially in Thailand. Progress of conventional breeding programs of grapevine for improved resistance to these diseases can be speeded up by selection of molecular markers associated with resistance traits. We evaluated the association between 13 resistance gene analog (RGA)-single-strand conformation polymorphism (SSCP) markers with resistance to downy mildew and anthracnose in 71 segregating progenies of seven cross combinations between susceptible cultivars and resistant lines. F(1) hybrids from each cross were assessed for resistance to downy mildew and anthracnose (isolates Nk4-1 and Rc2-1) under laboratory conditions. Association of resistance traits with RGA-SSCP markers was evaluated using simple linear regression analysis. Three RGA-SSCP markers were found to be significantly correlated with anthracnose resistance, whereas significant correlation with downy mildew resistance was observed for only one RGA-SSCP marker. These results demonstrate the usefulness of RGA-SSCP markers. Four candidate markers with significant associations to resistance to these two major diseases of grapevine were identified. However, these putative associations between markers and resistance need to be verified with larger segregating populations before they can be used for marker-assisted selection.

Evaluation of Grapevines for Resistance to Downy Mildew (Plasmopara viticola) under Laboratory and Field Conditions

Downy mildew of grapevine (Vitis vinifera L.), caused by the oomycete Plasmopara viticola, can seriously devastate grapevine production in tropical countries, such as Thailand. Four susceptible grapevine cultivars, four potentially resistant lines and 18 F1 hybrids, propagated by air layering and chip budding, were evaluated for resistance to downy mildew at laboratory (using a detached leaf assay) and field (natural infection in 2011 and 2013) levels. Significant differences in the disease scores among grapevine genotypes, ranging from 0.54 (resistant) to 4.83 (susceptible) and 3.30 (resistant) to 7.70 (susceptible), were observed under the laboratory and field conditions respectively. No significant difference in disease severity was observed between the two propagation methods or between the two different years of field evaluations. Resistance evaluations under both conditions consistently classified ‘NY88.0517.01’ and ‘NY65.0550.04’ as resistant lines what would be useful as parents for future breeding programmes. Moreover, one F1 hybrid, ‘SUT0403.09’, was reported to have considerable resistance to downy mildew under both laboratory and field conditions for the first time. The field resistance level of this hybrid was almost comparable to its highly resistant parent ‘Wilcox 321’, suggesting its potential for the future development of resistant cultivars in Thailand. Although the ranking of genotypes varied between screening methods, the resistance levels of the 26 grapevine genotypes evaluated under laboratory and field conditions were comparable based on the Spearman’s rank correlation coefficients of 0.73 (p ≤ 0.01). These results suggest that the laboratory screening assay is efficient for the rapid, reliable and economical identification of resistant hybrids in grapevine breeding programmes.

Application of ISSR markers for verification of F1 hybrids in mungbean (Vigna radiata)

Mungbean improvement via hybridization requires the identification of true F(1) hybrids from controlled crosses before further generations of selfing/crossing and selection. We utilized inter-simple sequence repeat (ISSR) markers for identifying putative F(1) hybrids from six cross combinations whose morphological characteristics were very similar to those of their respective female parents and could not be visually discriminated from the self-pollinated progeny. Based on 10 ISSR primers, polymorphisms were found between female and male parents of all six cross combinations. The highest value of genetic differentiation (21.4%) was found between male and female parents of the SUT3 x M5-1 cross. These 10 ISSR primers gave 2.8-25.0% polymorphism between male and female parents, with a mean of 12.1%, and 0-13.0% polymorphism between F(1) hybrid and female parents, with a mean of 4.8%. F(1) hybrids of all six cross combinations could be differentiated from the self-pollinated progeny of their female parents by using only either ISSR 841 or 857 primers, together with the ISSR 835 primer. We conclude that ISSR markers are useful and efficient for identifying mungbean F(1) hybrids in controlled crosses from different genetic background.

Morphological, pathogenicity and virulence characterization of Sphaceloma ampelinum the causal agent of grape anthracnose in Thailand

Grape anthracnose caused by Sphaceloma ampelinum is one of the most common fungal disease of grape in Thailand. The objective of this study was to examine the morphological diversity among Sphaceloma isolates from grapes and compare their pathogenicity and virulence on a susceptible grape cultivar. 24 isolates of Sphaceloma were isolated from diseased grape samples collected from different geographical regions of Thailand. Their colony morphology consisting of surface texture, elevation, aerial mycelium production, size and coloration were studied along with their conidial size. Subsequently 11 representative isolates having the same morphology were compared for their pathogenicity and virulence on Black Queen susceptible grape cultivar. According to the colours, the 11 isolates could be divided into 8 groups. The average colony size on potato dextrose agar measured at 35 days was 3.70 ± 0.10 × 3.82 ± 0.08 cm. Most isolates produced single – celled, hyaline, cylindrical shaped with rounded – end conidia containing a cellular gutter inside. The average conidial size was 2.1 to 3.6 × 3.4 to 6.7 μm. From the 11 isolates tested on Black Queen grapes, only 7 isolates had pathogenicity with different degree of virulence. Among the isolate GSH from the SUT farm, Nakorn Ratchasima was the most virulent.

Heterosis for the improvement of yield in mungbean [Vigna radiata (L.) Wilczek].

Heterotic effects of mungbean hybrids from 25 crosses between parents differing in 9 agronomic and physiological traits were evaluated for various selected traits and seed yield. Significant heteroses were observed in most selected traits, except for the number of seeds per plant. When the heterosis of seed yield was evaluated in these hybrids, significant heterosis was found in 9 crosses, which were selected based on the number of pods per plant, number of clusters per plant, pod length, number of seeds per pod, total dry matter, and root length density. These crosses may be exploited for mungbean yield improvement. Nine F8 lines from 2 of these 9 crosses (KPS 1 x V 2106 and SUT 1 x V 4785), a selection based on significant heterosis for seed yield and high seed yield of F1 and F2, which possessed a higher seed yield than their respective certified variety parents, were identified and these may be useful in future breeding programs.