Role of Ascorbate–Glutathione (AsA–GSH) Pathways in Phytophthora Leaf Blight Disease Resistance in Taro (Colocasia esculenta L. Schott)

Taro (Colocasia esculenta L. Schott) is one of the important staple vegetable crops grown worldwide for its nutritious corms, leaves, and pseudostems. Taro invaded by leaf blight disease caused by Phytophthora colocasiae Racib. (Pc) resulted in 50% yield loss. On the other hand, inherent defense mechanisms of taro encounter the invaders to protect the plant from Pc invasion. The ascorbate–glutathione (AsA–GSH) pathways play an essential role in scavenging reactive oxygen species (ROS), a common phenomenon in plant–pathogen interaction. The present study focused on AsA–GSH regulations of thirty genotypes of taro under induced Pc infection. RCMC–5, among the tested taro genotypes, registered consistently higher induction of AsA, GSH, Ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), and dehydroascorbate reductase (DHAR) to encounter the Pc infection and overproduction of ROS. However, glutathione reductase (GR) was more prominent in DP–25, Jhankri, and TSL. AsA–GSH encounters the ROS overproduction, which was confirmed with lower H2O2 (0.20 µM g–1 FW) and malondialdehyde (MDA) content (20.10 nM g–1 FW) in resistant genotypes (RCMC–5) subsequently resulted in lower Pc infection (spot diameter, <2.0 cm and sporangia, <2). RCMC–5 could be one of the lines of interest in taro breeding programs for developing Pc resistant lines. AsA–GSH cycle could be a reliable parameter while selecting resistant lines for augmenting breeding strategies in taro against Phytophthora.

Frequency of Resistant Western White Pine Seedlings from Parents of Different Phenotypes

Seedlings from different western white pine (Pinus monticola) parent phenotypes were inoculated with blister rust (Cronartium ribicola) to determine how they compared to the British Columbia standard candidate phenotype (canker-free with all branches retained) in their ability to produce resistant seedlings. Comparisons were separated into two seed zones, coastal and interior, as well as pooled. The phenotypic categories were: (1) standard candidate, (2) standard candidate except lacking lower branches, (3) standard candidate except for bark reactions in the stem, (4) standard candidate except for stem bark reactions and closer than 100 m to a similar candidate (Texada phenotype), (5) standard candidate except for a tolerant reaction to a basal canker, (6) standard candidate except for a single canker high in the crown, (7) normally cankered trees, (8) USDA Forest Service selections for Dorena, OR, and (9) bulked forest run seedlots. Open-pollinated offspring from parents were inoculated each fall from 1987-1995, and infection spots were tallied the following spring. All seedling infection spot values were normalized to seedlings from a control tree, which were included in each inoculation. The progeny from bulk seedlots and the Texada phenotype were significantly more spotted than the other phenotypes. The least spotted families (top 1/6) were predominantly from the standard, cankered, and bark-reaction phenotypes. Resistance of individual seedlings was detected by annual inspection and recording slow-canker-growth responses up to 7 yr post-inoculation. None of the progeny from bulk seedlots or the control exhibited slow canker growth. There was no significant difference among the progeny of the other eight parental phenotypes in the incidence of slow-canker-growth resistance. Of these eight, only normally cankered candidates failed to have any families rank in the top one-sixth for the most slow-canker-growth resistance. However, since the sample size was small for normally cankered, high cankered, and tolerant phenotype, the results are considered preliminarily. Since we consider slow-canker-growth resistance to be most useful, we recommended that future selection programs for parents include relaxed rule bark reaction and no lower branch phenotypes. West. J. Appl. For. 16(4):149-152.