Development of molecular markers linked to QTL/genes controlling Zn efficiency.

BACKGROUND: Zinc (Zn) deficiency is a widespread problem in reducing the yield and quality of crop plants worldwide. It is important to utilize molecular markers linked to Zn efficiency to develop high Zn efficient cultivars in pepper (Capsicum annuum L.). METHODS AND RESULTS: In present study, genetic map was constructed using a F2 populations derived from C. annuum L. (Alata 21A) × C. frutescens L. (PI 281420) cross. The quantitative trait locus (QTLs) for Zn efficiency were mapped using F2:3 population. A genetic map with 929.6 cM in length and 12 linkage groups were obtained using 62 markers (31 sequence-related amplified polymorphism (SRAP), 19 simple sequence repeat (SSR) and 11 random amplified polymorphic DNA (RAPD) markers). The 41 linked QTLs related with nine (9) Zn efficiency characters were mapped on linkage groups. Results suggest that selecting plants for tolerance to Zn deficiency are expected to be rather responsive among segregating populations for breeding and developing Zn efficient genotypes in pepper. CONCLUSIONS: The molecular markers are expected to aid selection and expedite breeding peppers resistant to Zn deficiency in soils low for available Zn contents.

Characterization of phenolics and tocopherol profile, capsaicinoid composition and bioactive properties of fruits in interspecies (Capsicum annuum X Capsicum frutescens) recombinant inbred pepper lines (RIL).

In this study, 104 RIL (Recombinant Inbred Pepper Lines: F6) populations which generated by selfing Capsicum annuum (Long pepper) × Capsicum frutescens (PI281420) F6 population were characterized in terms of detailed bioactive properties, major phenolic composition, tocopherol and capsaicinoid profile. Total phenolics, flavonoid and total anthocyanin contents of the red pepper lines were in the range of 7.06-17.15 mg gallic acid equivalent (GAE)/g dw, 1.10-5.46 mg catechin equivalent (CE)/g dw and 7.9-516.6 mg/kg dw extract, respectively. Antiradical activity and antioxidant capacity values also ranged between 18.99 and 49.73% and 6.97-16.47 mg ascorbic acid equivalent (AAE)/kg dw, respectively. Capsaicin and dihydrocapsaicin levels showed a wide variance with the range of 27.9-1405.9 and 12.3-640.4 mg/100 g dw, respectively. Scoville heat unit revealed that the 95% of the peppers were highly pungent. The major tocopherol was alpha tocopherol for the pepper samples with the highest level of 1078.4 µg/g dw. The major phenolics were detected as p-coumaric acid, ferulic acid, myricetin, luteolin and quercetin. Pepper genotypes showed significant differences in terms of the characterized properties and principal component analysis was applied successfully to reveal the similar genotypes.

Salt tolerance in Solanum pennellii: antioxidant response and related QTL.

BACKGROUND: Excessive soil salinity is an important problem for agriculture, however, salt tolerance is a complex trait that is not easily bred into plants. Exposure of cultivated tomato to salt stress has been reported to result in increased antioxidant content and activity. Salt tolerance of the related wild species, Solanum pennellii, has also been associated with similar changes in antioxidants. In this work, S. lycopersicum M82, S. pennellii LA716 and a S. pennellii introgression line (IL) population were evaluated for growth and their levels of antioxidant activity (total water-soluble antioxidant activity), major antioxidant compounds (phenolic and flavonoid contents) and antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) under both control and salt stress (150 mM NaCl) conditions. These data were then used to identify quantitative trait loci (QTL) responsible for controlling the antioxidant parameters under both stress and nonstress conditions. RESULTS: Under control conditions, cultivated tomato had higher levels of all antioxidants (except superoxide dismutase) than S. pennellii. However, under salt stress, the wild species showed greater induction of all antioxidants except peroxidase. The ILs showed diverse responses to salinity and proved very useful for the identification of QTL. Thus, 125 loci for antioxidant content under control and salt conditions were detected. Eleven of the total antioxidant activity and phenolic content QTL matched loci identified in an independent study using the same population, thereby reinforcing the validity of the loci. In addition, the growth responses of the ILs were evaluated to identify lines with favorable growth and antioxidant profiles. CONCLUSIONS: Plants have a complex antioxidant response when placed under salt stress. Some loci control antioxidant content under all conditions while others are responsible for antioxidant content only under saline or nonsaline conditions. The localization of QTL for these traits and the identification of lines with specific antioxidant and growth responses may be useful for breeding potentially salt tolerant tomato cultivars having higher antioxidant levels under nonstress and salt stress conditions.

Soybean Nodule-Associated Non-Rhizobial Bacteria Inhibit Plant Pathogens and Induce Growth Promotion in Tomato.

The root nodules are a unique environment formed on legume roots through a highly specific symbiotic relationship between leguminous plants and nodule-inducing bacteria. Previously, Rhizobia were presumed to be the only group of bacteria residing within nodules. However, recent studies discovered diverse groups of bacteria within the legume nodules. In this report soybean nodule-associated bacteria were studied in an effort to identify beneficial bacteria for plant disease control and growth promotion. Analysis of surface-sterilized single nodules showed bacterial diversity of the nodule microbiome. Five hundred non-rhizobial colonies from 10 nodules, 50 colonies per nodule, were tested individually against the tomato wilt causing bacterial pathogen Clavibacter michiganensis subsp. michiganensis (Cmm) for inhibition of pathogen growth. From the initial screening, 54 isolates were selected based on significant growth inhibition of Cmm. These isolates were further tested in vitro on another bacterial pathogen Pseudomonas syringae pv. tomato (Pst) and two fungal pathogens Rhizoctonia solani and Sclerotinia sclerotiorum. Bacterial metabolites were extracted from 15 selected isolates with ethanol and tested against pathogen Cmm and Pst. These isolates were identified by using MALDI-TOF mass spectrometry and 16S rRNA gene sequencing. Pseudomonas spp. were the dominant soybean nodule-associated non-rhizobial bacterial group. Several isolates imparted significant protection against pathogens and/or plant growth promotion on tomato seedlings. The most promising nodule-associated bacterial isolate that suppressed both Cmm and Pst in vitro and Pst in tomato seedlings was identified as a Proteus species. Isolation and identification of beneficial nodule-associated bacteria established the foundation for further exploration of potential nodule-associated bacteria for plant protection and growth promotion.

Engineered plant virus resistance.

Virus diseases are among the key limiting factors that cause significant yield loss and continuously threaten crop production. Resistant cultivars coupled with pesticide application are commonly used to circumvent these threats. One of the limitations of the reliance on resistant cultivars is the inevitable breakdown of resistance due to the multitude of variable virus populations. Similarly, chemical applications to control virus transmitting insect vectors are costly to the farmers, cause adverse health and environmental consequences, and often result in the emergence of resistant vector strains. Thus, exploiting strategies that provide durable and broad-spectrum resistance over diverse environments are of paramount importance. The development of plant gene transfer systems has allowed for the introgression of alien genes into plant genomes for novel disease control strategies, thus providing a mechanism for broadening the genetic resources available to plant breeders. Genetic engineering offers various options for introducing transgenic virus resistance into crop plants to provide a wide range of resistance to viral pathogens. This review examines the current strategies of developing virus resistant transgenic plants.