Sheath blight dynamics as affected by changes in microclimate and nitrogen application in different rice plant types

Pham Van Du

Date

11-1995

Abstract

Sheath blight disease is a major biotic constraint on rice production in intensive rice systems. It development has two typical phases, vertical and horizontal. Sheath blight development in relation to plant type, nitrogen application, and tropical microclimate needs to be better understood.

Three representative plant types, an early traditional rice cultivar (Soc Nau), a semidwarf indica cultivar (IR72) and a new rice plant type line (IR65600-164-3-2) which is being developed to further increase rice yield, were selected for the studies. Two separate field experiments were conducted, (1) to study sheath blight vertical development under 3 distinct plant type canopies, nitrogen levels and microclimate factors (2) and to study sheath blight horizontal development under 3 distinct plant type canopies, nitrogen application and 2 planting densities.

Experiments were done under irrigated lowland conditions during wet season (WS) 1994. The experiments were split-plot design in a randomized complete block (RCB) with three replications for first and four replications for the second experiment.

Plant type structural characteristics such as plant height, tillering capacity, leaf area, number of leaves, leaf and culm angle and above plant dry weight were found to be significantly different between the 3 plant types, and nitrogen levels, with the exception of leaf angle and culm angle. The cultivar Soc Nau had the largest plant type characteristics while the IR65600-164-3-2 line had the lowest tillering capacity, number of leaves and above plant dry weight. Nitrogen content (%) in different plant organs was significantly different between plant types and nitrogen applications. Highest nitrogen content was in IR65600-164-3-2 line, while cultivar Soc Nau had the lowest nitrogen content. Leaf and stem nitrogen content were found to decline from 40 DAT up to harvest. Canopy microclimate factors such as light transmission ratio, within canopy temperature and relative humidity and leaf wetness duration were found significantly different among modified canopies.

Sheath blight vertical development was measured using highest relative lesion height (HRLH) and relative atual lesio lenght (RALL). Cultivar IR72 had the highest HRLH, Soc Nau had the lowest HRLH. In terms of RALL, IR65600-164-3-2 had the highest value among the 3 plant types because of more lesions on stems and greater lesion expansion. RALL was more precise than HRLH particularly when measuring sheath blight, vertical development among plant type. Levels of N from 40 to 160 kg/ha showed significant difference in area under HRLH and RALL.

Results from path analysis showed that direct effect of nitrogen content (%) on structural variables of 3 plant types and sheath blight vertical development. Consequently, modified plant type canopies had direct effects on canopy microclimate.

Sheath blight horizontal development was evaluated from 72 foci at two planting densities , 20 x 20 and 20 x 10 cm. Results from the study showed that sheath blight horizontal spread was affected by plant types and planting densities, but not by nitrogen levels. Sheath blight can spread 110 cm from the focus on canopy IR72,60 cm on IR65600-164-3-2 and 50cm on canopy Soc Nau. Canopy contact frequencies determined the "spread pattern" of sheath blight. Canopy microclimate variables such as light transmission ratio, within canopy temperature and relative humidity were most important for sheath blight horizontal spread. Without these conducive factors, horizontal spread cannot occur.

Document Type

Dissertation

Degree

Doctor of Philosophy in Plant Pathology

College

Graduate School (GS)

Adviser/Committee Chair

Avelino D. Raymundo

Co-adviser

Paul S. Teng

Committee Member

Restituta P. Robles, Oscar S. Opina

Language

English

LC Subject

Rice sheath blight Rice--Diseases and pests

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 P57 P43

Notes

Doctor of Philosophy (Plant Pathology)

This document is currently not available here.

Share

COinS