Transgressive variants for red pericarp grain with high yield potential derived from Oryza rufipogon × Oryza sativa: Field evaluation, screening for blast disease, QTL validation and background marker analysis for agronomic traits

Five transgressive variants (advanced breeding lines from BC₂F₅ and BC₂F₆ generation) were derived from a cross between the wild relative, O. rufipogon Griff. and O. sativa L. subsp. indica cv. MR219, a popular high yielding Malaysian rice cultivar. The aim of the study was to evaluate the pericarp colour of the grains along with yield potential and to validate quantitative trait loci (QTLs) for agronomic traits. The variants were screened against blast disease. Background marker analysis was also done for the promising variants. The field trials were carried out at a single location (due to containment purposes) over two seasons using randomized complete block design (RCBD) with three replications. A trait-based marker analysis was used to identify QTLs for validation in BC₂F₅ generation. Analysis of variance (ANOVA) showed that the seasonal factors influenced different agronomic traits. Variant G33 produced significantly (p < 0.05) higher yield (5.20 t/ha) than the control, MR219 (4.53 t/ha). Eighteen QTLs for different agronomic traits were identified in BC₂F₂ population in a previous study. Among them 14 QTLs were found in BC₂F₅ population of the present study. The yield of variant G33 was influenced by several QTLs viz. qGPL-1, qSPL-1-2, qSPL-8 and qYLD-4, which were introgressed from the donor parent revealed by background marker analysis using BC₂F₇ generation. Percentage (99%) of red pericarp grain of G33 and G34 in BC₂F₅ and BC₂F₆ generations indicated the stability of pericarp colour which was transferred from the wild relative. Variant G33 showed resistance against two pathotype of blast disease (Magnaporthe oryzae). Among the evaluated variants, G33 could be considered for inclusion in the cultivar development program for red rice with high yield potential and resistance to blast disease. This study demonstrated that the alleles from wild relative could improve the yield and yield related traits through allelic interaction, even though the phenotypic traits were inferior to the recurrent parent.     

Genotypic variation for root traits of maize (Zea mays L.) from the Purhepecha Plateau under contrasting phosphorus availability

Phosphorus (P) deficiency is a major constraint for maize production in many low-input agroecosystems. This study was conducted to evaluate genotypic variation in both root (root architecture and morphology, including root hairs) and plant growth traits associated with the adaptation of maize landraces to a P-deficient Andisol in two locations in the Central Mexican highlands. Two hundred and forty-two accessions from the Purhepecha Plateau, Michoacan were grown in Ponzomaran with low (23 kg P₂O₅ ha⁻¹) and high (97 kg P₂O₅ ha⁻¹) P fertilization under rain-fed field conditions, and subsequently a subset of 50 contrasting accessions were planted in the succeeding crop cycle in Bonilla. Accessions differed greatly in plant growth, root morphology and P efficiency defined as growth with suboptimal P availability. The accessions were divided into 3 categories of P efficiency using principal component and cluster analyses, and 4 categories according to the retained principal component and their relative weight for each genotype in combination with growth or yield potential. The distribution of accessions among three phosphorus efficiency classes was stable across locations. Phosphorus-efficient accessions had greater biomass, root to shoot ratio, nodal rooting, nodal root laterals, and nodal root hair density and length of nodal root main axis, and first-order laterals under P deficiency. Biomass allocation to roots, as quantified by the allometric partitioning coefficient (K) was not altered by P availability in the efficient accessions, but inefficient accessions had a lower K under low P conditions. Accessions with enhanced nodal rooting and laterals had greater growth under low P. Dense root hairs on nodal root main axes and first-order laterals conferred a marked benefit under low P, as evidenced by increased plant biomass. Late maturity improved growth and yield under low P. These results indicate that landraces of the Central Mexican highlands exhibit variation for several root traits that may be useful for genetic improvement of P efficiency in maize.     

甜菜重要农艺性状的数量性状基因座(QTL)研究进展

阐述了农作物数量性状基因座(QTL)在遗传育种中的地位和意义,介绍了作物QTL的基本原理和方法及在甜菜上的研究进展。     

Response of maize (Zea mays L.) to post-emergence applications of topramezone

Topramezone is a new herbicide for post-emergence control of broadleaf and grass weeds in maize. Two field experiments were conducted in northern Greece in 2008 and 2009 to determine the response of grain maize to topramezone applied with the adjuvant DASH at 2–4, 4–6 and 6–8 maize leaf stage. In both years, plant height, cob number and yield were not differently affected with the use of herbicide at these growth stages, indicating no difference in selectivity and a similar response of maize to the three post-emergence applications of topramezone. Slight injury symptoms of leaf bleaching were observed in the second year, however, they were transient with no lasting injury on maize growth.     

The large-effect drought-resistance QTL qtl12.1 increases water uptake in upland rice

Drought stress is the most important abiotic factor limiting upland rice yields. Identification of quantitative trait loci (QTL) conferring improved drought resistance may facilitate breeding progress. We previously mapped a QTL with a large effect on grain yield under severe drought stress (qtl12.1) in the Vandana/Way Rarem population. In the current paper, we present results from a series of experiments investigating the physiological mechanism(s) by which qtl12.1 affects grain yield under drought conditions. We performed detailed plant water status measurements on a subset of lines having similar crop growth duration but contrasting genotypes at qtl12.1 under field (24 genotypes) and greenhouse (14 genotypes) conditions. The Way Rarem-derived allele of qtl12.1 was confirmed to improve grain yield under drought mainly through a slight improvement (7%) in plant water uptake under water-limited conditions. Such an apparently small increase in water uptake associated with this allele could explain the large effect on yield observed under field conditions. Our results suggest that this improvement of plant water uptake is likely associated with improved root architecture.     

Kernel amino acid composition and protein content of introgression lines from Zea mays ssp. mexicana into cultivated maize

Development of high yield maize germplasm with satisfying nutritional quality has been a major objective for maize breeders. Introgression lines from hybrids between Zea mays ssp. mexicana, a close wild relative of cultivated maize, and elite maize inbred line Ye515 were obtained. Ear-related traits of the lines showed wide range of variation compared to the maize parent. Kernel protein contents in the progeny lines ranged from 7.89% to 12.44%. Considerable variability of protein fractions and amino acid composition of mature endosperms was observed. Protein contents for some lines such as SD00362, SD00312 and SD00259 were significantly higher than that of Ye515, and Lys and some other essential amino acids were conspicuously improved. It was concluded that introgression from Z. mays ssp. mexicana into a maize background had great effects on protein content and composition, and that desirable inbred lines with enhanced protein contents and improved nutritional value were produced via alien introgression.     

Effect of N supply on stalk quality in maize hybrids

The identification of maize nitrogen (N) response for stalk quality is valuable in stalk breeding improvement, stalk lodging resistance and for use in bioenergy. This study analyzed the effect of two N levels and estimated quantitative genetic parameters for stalk quality in summer maize in the north China plain (NCP). Thirty hybrids were sampled and tested from three to four geographic locations under high nitrogen (HN) (225 kg N ha⁻¹) and low nitrogen (LN) (0 kg N ha⁻¹) during 2006–2008. Compared to HN level, stalk crude protein (CP) was significantly reduced (22.06%) under LN level. Ether extract (EE), ash content (AC), in vitro dry matter digestion (IVDMD) and lignin content (LC) were lower under LN level. Cellulose content (CC), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were increased with a reduction in N, however N did not significantly affect EE, ADF and LC. An increase in NDF and ADF content under low vs. high N level was mainly attributed to a reduction in CC. ADF and NDF exhibited positive correlation and both showed a positive correlation with CC but a negative correlation with LC, IVDMD and CP. Negative correlations between IVDMD and CC, IVDMD and LC, and CP and CC were also detected. The interaction variance of genotype × year × location (σ²_GYL) for each N level, with the exception of σ²_GYL for CC under HN, was significant and most stalk quality traits were evaluated in different locations and years. The estimates of genetic variance (σ²_G) and heritability (h²) were greater under HN, with the exception of LC and EE. The interaction of genotype × nitrogen (σ²_GN) for CP was more important than σ²_G. The genotypic correlation coefficients (r_G) for performance in different stalk quality traits between HN and LN were significant. However, it was necessary to evaluate both HN and LN for IVDMD. For other stalk quality traits, breeding maize under HN levels may serve to develop hybrids well adapted to high and/or low N level. The response to N trend was similar between high oil and normal maize hybrids.     

Characterization of Solanum chomatophilum resistance to 2 aphid potato pests, Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer)

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) are responsible for yield reduction in potato (Solanum tuberosum) production by direct phloem feeding and by spreading viruses. Breeding resistant traits from Solanum chomatophilum into the potato germplasm provides alternative means to control aphid infestations. Integrated pest management strategy, using plant resistance, benefits from the characterization of the resistance and of its impact on aphid biology. Our objective was to characterize the resistance of S. chomatophilum by assessing the effects of accessions, plant parts on aphid performance, and by assessing the impact of the resistance factors on different aphid developmental stages and on alate morph production. Detailed aphid performance was obtained by measuring fecundity, survival, percentage of nymphs that reached adult moult, and population growth using whole plant and clip cage experimental designs. Accession and plant physiological age, but not aphid developmental stage, influenced all life-history parameters, except for alate morph production which was not induced on the resistant accessions. Plant part influence was independent of plant species and accession. Both experimental designs resulted in congruent resistance levels at the accession level for each of the two aphid species, supporting the use of any of them in S. chomatophilum resistance screening. PI243340 was resistant to both aphid species, while PI365324 and PI310990 were also resistant to M. euphorbiae and M. persicae, respectively.     

Maize genotype susceptibility to Rhizoctonia solani and its effect on sugar beet crop rotations

Root and crown rot is the major soil-borne fungal disease in sugar beet. In Europe, the disease is mainly caused by the anastomosis group (AG) 2-2IIIB of the basidiomycete Rhizoctonia solani (Kühn). No chemical fungicide to control the disease has been registered in Europe. Therefore, agronomic measures must be optimized to keep the disease severity below an economic damage threshold and to minimize white sugar yield losses. R. solani AG 2-2IIIB infects many other crops besides sugar beet, including maize, where it causes root rot. Sugar beet and maize are frequently grown in the same crop rotation. The proportion of cultivated maize in several European sugar beet growing areas is expected to rise due to a projected increase in demand for renewable resources over the next few years. Although the susceptibility to and tolerance of the disease varies among cultivars in both crops, little is known about the effects of cultivar susceptibility in the pre-crop on a subsequent susceptible crop. The cultivation of R. solani-resistant maize genotypes in rotation with resistant sugar beet might therefore be a useful tool in an integrated control strategy against R. solani, eliminating the need to restrict the desired crop rotation for phytosanitary reasons. A crop rotation experiment with artificially inoculated R. solani was conducted in the field to investigate the pre-crop effects of maize cultivars which differed in their susceptibility to R. solani on a susceptible sugar beet cultivar. We hypothesized that the maize genotype would influence the inoculum potential and performance of a susceptible sugar beet genotype grown after a maize pre-crop, and that this would correlate with the susceptibility of the maize genotype. The results demonstrate that the susceptibility of maize genotypes is consistent over a period of years and that cultivated maize genotypes influenced the inoculum potential measured as disease severity in sugar beet. However, disease severity in sugar beet did not correlate with the disease susceptibility of the genotype of the maize pre-crop. Possible reasons for this missing relationship might be differences in the quality of maize residues for the saprophytic survival of the pathogen or a genotype-specific alteration of the antagonistic microbial community. However, our findings showed that in the presence of maize- and sugar beet-pathogenic R. solani, the most favourable maize cultivar for a crop rotation cannot be determined solely on the basis of its resistance level against Rhizoctonia root rot.     

Damage and survivorship of fall armyworm (Lepidoptera: Noctuidae) on transgenic field corn expressing Bacillus thuringiensis Cry proteins

Field corn, Zea mays L., plants expressing Cry1Ab and Cry1F insecticidal crystal (Cry) proteins of Bacillus thuringiensis (Bt) Berliner are planted on considerable acreage across the Southern region of the United States. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is an economically important pest during the mid-to-late season on non-Bt and some commercial Bt corn hybrids. The objective of this study was to quantify foliar injury and survivorship of fall armyworm on transgenic corn lines expressing Cry1Ab or Cry1F Bt proteins. Corn lines/hybrids expressing Cry1Ab, Cry1F, and a conventional non-Bt cultivar were evaluated against artificial infestations of fall armyworm in field trials. Larvae (second instars) of fall armyworm were placed on corn plants (V8-V10 stages). Leaf injury ratings were recorded 14 d after infestation. Hybrids expressing Cry1F had significantly lower feeding injury ratings than non-Bt corn plants. Development and survivorship of fall armyworm on Bt corn lines/hybrids were also evaluated in no-choice laboratory assays by offering freshly harvested corn leaf tissue to third instars. Transgenic corn hybrids expressing Cry1Ab or Cry1F significantly reduced growth, development, and survivorship of fall armyworm compared to those offered non-Bt corn tissue. However, 25-76% of third instars offered Bt corn leaf tissues successfully pupated and emerged as adults. These results suggest Cry1Ab has limited effects on fall armyworm; whereas Cry1F demonstrated significant reductions in foliar injury and lower survivorship compared to that on non-Bt corn tissues. Although fall armyworm is not considered a primary target for insect resistance management by the U.S. Environmental Protection Agency, these levels of survivorship could impact selection pressures across the farmscape, especially when considering that transgenic Bt cotton cultivars express similar Cry (Cry1Ac or Cry1F) proteins.     

High level of resistance to Sclerotinia sclerotiorum in introgression lines derived from hybridization between wild crucifers and the crop Brassica species B. napus and B. juncea

Sclerotinia rot caused by the fungus Sclerotinia sclerotiorum is one of the most serious and damaging diseases of oilseed rape and there is keen worldwide interest to identify Brassica genotypes with resistance to this pathogen. Complete resistance against this pathogen has not been reported in the field, with only partial resistance being observed in some Brassica genotypes. Introgression lines were developed following hybridization of three wild crucifers (viz. Erucastrum cardaminoides, Diplotaxis tenuisiliqua and E. abyssinicum) with B. napus or B. juncea. Their resistance responses were characterized by using a stem inoculation test. Seed of 54 lines of B. napus and B. juncea obtained from Australia, India and China through an Australian Centre for International Agricultural Research (ACIAR) collaboration programme were used as susceptible check comparisons. Introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum had much higher levels (P < 0.001) of resistance compared with the ACIAR germplasm. Median values of stem lesion length of introgression lines derived from the wild species were 1.2, 1.7 and 2.0 cm, respectively, as compared with the ACIAR germplasm where the median value for stem lesion length was 8.7 cm. This is the first report of high levels of resistance against S. sclerotiorum in introgression lines derived from E. cardaminoides, D. tenuisiliqua and E. abyssinicum. The novel sources of resistance identified in this study are a highly valuable resource that can be used in oilseed Brassica breeding programmes to enhance resistance in future B. napus and B. juncea cultivars against Sclerotinia stem rot.     

利用F2:3群体对玉米花期相关性状的QTL分析

以玉米自交系四287与四144为亲本的188个F_2:3家系为材料, 考察玉米花期相关性状, 并利用该群体的分子遗传连锁图谱进行QTL分析。结果表明, 共检测到11个与玉米花期相关的QTL, 包括与抽雄期相关的2个QTL, 位于第3和第8染色体上, 贡献率分别为21.9%和13.6%;与散粉期相关的3个QTL, 位于第1、3和第8染色体上, 贡献率分别为14.8%、21.0%和18.5%;与吐丝期相关的2个QTL, 位于第3和第8染色体上, 贡献率分别为16.5%和20.1%;与散粉-吐丝间隔期相关的4个QTL, 位于第1、6、7和第8染色体上, 贡献率分别为23.5%、25.3%、28.9%和20.9%。这些QTL的基因效应以部分显性和显性为主。     

Comparative susceptibility of Ostrinia furnacalis, Ostrinia nubilalis and Diatraea saccharalis (Lepidoptera: Crambidae) to Bacillus thuringiensis Cry1 toxins

Transgenic corn hybrids that express toxins from Bacillus thuringiensis (Bt) are highly effective against the European corn borer, Ostrinia nubilalis (Hübner), and the closely related Asian corn borer, Ostrinia furnacalis (Guenée). Since the registration of Bt corn hybrids in the U.S. in 1996, there has been a great deal of information generated on O. nubilalis. However, relatively little information exists for O. furnacalis. To help determine whether the information generated for O. nubilalis can be leveraged for decisions regarding the use of transgenic Bt corn against O. furnacalis, experiments were designed to determine whether the pattern of sensitivity to various Bt Cry1 toxins is similar between the two species. Test insects included laboratory-reared O. furnacalis originating from Malaysia, a Bt-susceptible laboratory colony of O. nubilalis maintained at the University of Nebraska-Lincoln (UNL) and an out-group consisting of the sugarcane borer, Diatraea saccharalis (F.), from Louisiana which represents a different genus from the same family. O. furnacalis and O. nubilalis exhibited a similar pattern of susceptibility to all the Cry1 toxins and were highly susceptible to the range of Bt toxins tested including Cry1Aa, Cry1Ab, Cry1Ac and Cry1F. Both of the Ostrinia species were more tolerant to Cry1Ba compared with D. saccharalis, although sensitivity of O. furnacalis was intermediate and did not differ significantly from that of O. nubilalis and D. saccharalis. D. saccharalis was also susceptible to the range of toxins tested but unlike the two Ostrinia species, was more tolerant to Cry1F and more susceptible to Cry1Ba. These results indicate that both of the Ostrinia corn borer species are similar in sensitivity to the Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1F toxins, thus suggesting shared toxin receptors and mechanisms of toxicity for the two species.     

QTL underlying plant and first branch height in cassava (Manihot esculenta Crantz)

Cassava, Manihot esculenta Crantz subsp. Esculenta was a major food crop across Asia and Africa. The crop was a highly heterozygous perennial woody shrub cultivated from stem cuttings. Cassava improvement for starchy tuberous roots requires about 5-6 years from F₁ hybrid seed germination to the selection of superior genotypes. Early selection with DNA markers could increase the number of elite genotypes identified. The aim here was to identify DNA markers associated with loci underlying plant and first branch height. In this study, 640 SSR primer pairs were used to screen for polymorphisms in two parental lines, cv. ‘Huaybong60’ (female) and cv. ‘Hanatee’ (male). There were 235 informative polymorphic markers used to genotype 100 individuals of an F₁ mapping population. Genotype data was analyzed by JoinMap^® version 3.0 software in order to construct a genetic linkage map. The map consisted of 156 linked SSR markers distributed across 25 linkage groups. The total length of the map was 845.2 cM (Kosambi cM) with 6.2 loci per linkage group, and an average distance between markers of 7.9 cM. Plant and first branch height of stem cuttings from the F₁ mapping population were collected from individual lines planted in 2007-2009. Quantitative Trait Loci (QTL) underlying these traits were identified using mapQTL^®/version 4.0. A total of seven QTL placed on four linkage groups were found for plant height. Of these, one major QTL was discovered on linkage group 2 near the marker SSRY155 with 17.9% of phenotypic variation explained (PVE). For first branch height, five QTL located on five linkage groups were identified. The two major QTL were located on linkage groups 2, and 20 at the loci SSRY323 and SSRY236 with 23.5% and 22.6% PVE, respectively. The QTL for plant and first branch height will serve as useful molecular markers in a cassava breeding program and may allow identification of the underlying genes in future.     

Evaluations of shallot genotypes for resistance against fusarium basal rot (Fusarium oxysporum f. sp. cepae) disease

Fusarium basal rot (FBR) caused by Fusarium oxysporum f. sp. cepae (Foc) is one of the most significant production constraint to shallot. Field experiment was conducted in a naturally Foc infested soil at Debre Zeit Agricultural Research Center during 2006 and 2007 cropping seasons to evaluate the level of resistance of sixteen shallot genotypes against FBR disease. Treatments were arranged in randomized complete block design with four replications. The genotypes significantly varied in their susceptibility to FBR and yield. They were grouped into tolerant, moderately and highly susceptible types. Five genotypes (DZ-Sht-168-1A, DZ-Sht-157-1B, Huruta, Negelle and DZ-Sht-169-1b) were identified to be tolerant as they had reduced disease severity levels from 26.8 to 32.5% and increased mean yield by more than 5 t ha⁻¹ compared to highly susceptible genotypes (DZ-Sht-076-4, DZ-Sht-201-1C and DZ-Sht-054-3A). Among the tolerant genotypes, DZ-Sht-169-1b had greatly reduced bulb rot incidence by 48% in ground storage and 30% in wire mesh shelf as compared to highly susceptible genotype DZ-Sht-201-1C. The tolerant genotypes have high yielding characteristic, and farmers could adopt them for cultivation where FBR is a problem.     

Morpho-physiological traits associated with maize crop adaptations to environments differing in nitrogen availability

The use of genotypes with improved performance for nitrogen (N) capture and use would be of great benefit through reducing production costs and pollution risks in maize cropping. The identification of morpho-physiological traits responsible for a better behavior in a target N environment is useful for cultivar selection, and become crucial for maize breeding improvement. This study analyzed, in a set of Argentinean commercial hybrids of maize, the grain yield (GY) variability in response to soil N availability at several locations representative of the main maize production region of Argentina during 2003–2004 growing season. The objectives of this work were to: (i) detect environmental groups for GY responses, (ii) identify morpho-physiological traits that were associated to winner genotypes in each detected environmental group, and (iii) assess genetic correlations between those traits. To generate more variation in soil N availability two N-fertilizer rates were applied in each experimental site (0 and 250 kg N ha⁻¹, except for Balcarce where only 250 kg N ha⁻¹ was tested). Morpho-physiological traits included in the analysis were related to N and radiation capture, use and partitioning, plant architecture, and leaf senescence. Grain yield components were also included. As expected, environment (E) effect explained the higher portion of GY variation (i.e., 82%), but genotype (G) and G × E interaction (GE) also significantly contributed (i.e., 9% each). Three environmental groups for GY were identified according to N availability. Morpho-physiological traits related to resource capture, use, and partitioning during the post-silking period are proposed as desirables for broad adaptation. In turn, a high N partitioning to grains after silking was associated with good hybrid behavior under high N availability and warm climate. On the other hand, a better grain yield performance when N became more limited appeared strongly related to an efficient canopy to sustain resource capture up to maturity. More studies are required in a wide range of environments to confirm identified traits and underlying physiological mechanisms. Nevertheless, our findings highlight the existence of differences in ideal plant-type for environments differing in N availability to be considered in maize breeding programs.     

Swiss Flint maize landraces—A rich pool of variability for early vigour in cool environments

Today's modern Dent × Flint maize (Zea mays L. ssp. mays) hybrids have a high yield potential but often lack satisfying early vigour under typical low spring temperatures of temperate latitudes. Maize was introduced into Europe already in the 16th century and until the 1950s, landraces evolved and adapted well to various geographically restricted and climatically marginal regions in Europe. Therefore, the objective of this study was to assess representatives of the large pool of Swiss Flint maize landraces for their early vigour under cool conditions in the field. A set of 17 landrace accessions were tested for 2 years at sites on the Swiss plateau (450 and 550 m a.s.l.) and in the foothills of the Swiss Alps (830 and 870 m a.s.l.). Plant emergence (PE), emergence index (EI), the efficiency of the photosystem II (F_v/F_m), leaf greenness (SPAD) and plant dry weight at the three- and six-leaf stages (DW3_P, DW6_P) were measured.     

水稻柱头外露率的QTL分析

以高柱头外露率的50S作母本,低柱头外露率的三系粳稻保持系连B作父本杂交,种植F2群体,调查单株调查柱头外露率,分析表明群体柱头外露率值接近正态分布;以SSR标记建立了该群体的基因分子连锁图谱,使用该群体分子连锁图谱进行柱头外露率的QTL分析,共检测到3个控制水稻柱头外露率的QTL(qPES-3,qPES-9,qPES-12),分别位于第3、第9、第12染色体,其增效基因均来自50S。并对选育高柱头外露率粳稻保持系进行了探讨。     

Effect of Acibenzolar-S-methyl (ASM) pre-treatment in inducing resistance against Pythium aphanidermatum infection in Curcuma longa

In vitro experiments were carried out to test the efficacy of plant activator Acibenzolar-S-methyl (ASM, a benzothiadiazole derivative; trade name Bion 50WG) against rhizome rot disease of turmeric (Curcuma longa L.) caused by Pythium aphanidermatum. The plant activator was applied as a liquid rhizome pre-treatment followed by inoculation with P. aphanidermatum. Cell death, activities of pathogenesis related (PR) proteins such as cysteine protease (EC 3.4.22), peroxidases (EC 1.11.1.7) both soluble and ionically bound (IB), trypsin inhibitor (EC 3.4.21.1) and chymotrypsin inhibitor (EC 3.4.21.4) were monitored. Rhizome pre-treatment was effective in controlling P. aphanidermatum infection. Anatomical observation of turmeric rhizomes indicated the presence of calcium oxalate deposits in infected tissue and an accumulation of starch grains in response to infection by P. aphanidermatum. Pathogen infection also induced new basic polypeptides corresponding to 18.0 and 41.0 kDa. Induction of protease, protease inhibitors, soluble and ionically bound peroxidase activity was observed after ASM pre-treatment and P. aphanidermatum infection. ASM treatment also enhanced activities of proteases and peroxidase in rhizomes already infected with P. aphanidermatum. Increases in enzyme activities and protease inhibitors occurred much more rapidly and were enhanced in P. aphanidermatum infected rhizomes that were previously treated with ASM suggesting that increased activities of peroxidases and protease inhibitors may play a key role in restricting the development of disease symptoms on the rhizomes infected with P. aphanidermatum as evidenced by a reduction in cell death. Hence, pretreatment with ASM suppress the P. aphanidermatum induced oxidative damage through higher accumulation of peroxidases and induced defense through activities of protease inhibitors thereby, protected turmeric rhizomes from rhizome rot disease.     

Manihot flabellifolia Pohl,wild source of resistance to the whitefly Aleurotrachelus socialis Bondar (Hemiptera: Aleyrodidae)

Aleurotrachelus socialis is one of the most important pests of cassava (Manihot esculenta Crantz) in the Neotropics. In Colombia, high whitefly populations can reduce crop yields by 79%; and although the farmers intensify the use of insecticides, this practice is highly contaminating, costly and leads to the development of resistance in the insect. An alternative for managing whitefly populations is to develop genetically resistant varieties. Wild parents of Manihot are a useful source of genes against pests for the cultivated species of cassava. Based on prior research that showed the existence of moderate-to-high levels of resistance to A. socialis in Manihot flabellifolia, a wild species of cassava, this study was proposed to characterize this new source of resistance, evaluating the biology and demographics of A. socialis on eight accessions of M. flabellifolia, a susceptible check (CMC-40) and a resistant (MEcu72) check. The averages of A. socialis longevity and fecundity on the accessions were not significantly different to MEcu72, but different from CMC-40 (P < 0.05). Development time was not significantly different, ranging from 35–40 days on accessions and MEcu72 and 33.5 days on CMC-40 (P < 0.05). In contrast, the population growth rate (r_m) was significantly lower on the M. flabellifolia accessions, with Fla 61 standing out with a growth rate 98 and 99% less than that obtained on MEcu72 and CMC-40, respectively. Once the resistant levels have been identified to A. socialis on the M. flabellifolia accessions, interspecific crosses of M. esculenta subsp. M. flabellifolia and backcross programs could be developed to incorporate the desirable characteristics from the wild relatives into elite progenitors of M. esculenta.