Johnson K. George

Biochemical variation in turmeric (Curcuma longa Linn.) accessions based on isozyme polymorphism

SummaryFifteen accessions of Curcuma longa L. collected from different geographical areas in India, along with a few seedling progenies, were studied for variation based on isozyme polymorphism. A high degree of variability (63.8–96% similarity) was seen in the population studied. Phenetic analyses revealed several groups with interesting features. Two seedling progenies, which showed maximum similarity, stood distinctly from the clonally propagated material. Other pairs of accessions showing high similarity (above 90%), were from the same geographical area, indicating that accessions collected based on vernacular names and those collected from adjoining areas, need not be genetically distinct.

CHARACTERIZATION OF TWO INTERSPECIFIC HYBRIDS OF PIPER

SummaryTwo interspecific hybrids of Piper, P. nigrum x P. attenuatum and P. nigrum x P. barberi, produced for the first time, were characterized by morphology, anatomy, isozymes, cytology and function (reaction to pollu beetle). The hybrids exhibit distinct morphological and anatomical features. Hybrid-specific bands as well as male-specific bands were observed in the zymograms of the isoforms of three of the four isozymes, peroxidase, esterase and polyphenol oxidase. Paired affinity index of the four enzymes revealed more similarity between the female parents and hybrids than between the male parents and hybrids. The hybrids had the same chromosome number (2n.=.52) as their parents. The leaves of the hybrids were less preferred for feeding by pollu beetles when compared with their female parents. Successful hybridization among the three species belonging to the same subgenus Maricha confirms their phylogenic relationship.

Occurrence, distribution and economic potential of seashore mangosteen (Garcinia hombroniana Pierre) in India

Seashore mangosteen (Garcinia hombroniana Pierre), an important component of Garcinia gene pool, is useful as a rootstock and also in the genetic improvement of mangosteen. A brief description along with short notes on distribution and uses is given. Naturally occurring in Nicobar Islands and under cultivation in Tamil Nadu and Kerala, its germplasm needs to be collected and conserved for its potential horticultural value.

Resistance Genes in Piper colubrinum: In Silico Survey From Leaf Transcriptome and Expression Studies Upon Challenge Inoculation with Phytophthora capsici

The oomycetes, Phytophthora capsici, cause foot rot disease in black pepper. Piper colubrinum Link, a distant relative of cultivated black pepper, is highly resistant to this destructive pathogen. Identification of resistance (R) genes in P. colubrinum and the study of its expression profile during interaction with the pathogen can help in understanding the resistance mechanism involved. In the present study, 1289 R gene-related transcripts were mined from P. colubrinum transcriptome, clustered, and classified according to the conserved motifs and domains. Transcripts belonging to four major R gene classes were identified in P. colubrinum, but TIR-NBS-LRR-type R genes were absent. The relative expression of 12 selected R genes was studied using two virulent isolates of P. capsici, and these were found to be upregulated in the initial hours of plant pathogen interaction. The R genes studied were expressed even in aseptically maintained tissue-cultured plants and uninoculated greenhouse-grown plants at basal level suggesting that the plants are geared up with the R gene all the time and are under continuous surveillance for the pathogen and basal level of R gene expression do not require a pathogen trigger. ACT, ATUB, and EIF3E were identified as the most stable reference genes that can be used for real-time PCR study. The present study identified promising R genes in P. colubrinum which can be used in developing Phytophthora-resistant black pepper.

Black Pepper and Water Stress

Black pepper is mainly grown as a rainfed crop. Total rainfall and its distribution influence pepper productivity. Heavy rains during flowering reduce the rate of pollination and continuous heavy rainfall promotes vegetative development and limits flowering. On the other hand, break in the rainfall experienced at different stages during critical period following flower initiation leads to severe reduction in yield. Black pepper needs to be irrigated in summer to harvest good crop. Low spike intensity in rainfed situation is due to staggered and delayed spiking, lower bisexual flowers, anthracnose incidence, and spike shedding. Both plant height and leaf area are affected by water stress. Tolerant genotypes maintain higher root growth, higher relative water content, and lower cell membrane leakage under stress condition. In general, tolerant genotypes accumulated all the amino acids in higher quantities compared to susceptible ones during water stress. A, gs, and E decreased drastically, while Tleaf increased after 6 days of stress induction. Water stress reduced the activity of catalase and acid phosphatase and increased the activities of peroxidase, glutathione reductase, and polyphenol oxidase enzymes. Lipid peroxidation was high in drought-susceptible cultivars compared to tolerant cultivars. There was no difference in the expression profile of isoforms of catalase and peroxidase enzymes between control and stress, while super oxide dismutase showed an additional isoform in some genotypes under stress condition. Studies on 2D SDS gel electrophoresis indicated that the proteins relevant to photosynthesis were downregulated during drought suggesting reduced photo oxidative stress and protection of photosynthetic machinery during stress. Studies on exogenous application of ABA indicated a role for ABA in stress tolerance.