Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Master of Science (MS)

Department / School

Plant Science

Abstract

Early season crop-weed interaction influences com growth that will result to reduced yield during a critical weed-free period (CWFP). Yield loss is not mitigated by weed removal after the CWFP, hence, weeds cause an irreversible negative impact on growth and development during the CWFP. However, CWFP in com is not consistent across sites and years. In addition, mechanisms that brought about yield loss during the CWFP are not well understood. This study determined the critical weed-free period in com and examined the impact of early-season weed (canola, grass, or velvetleaf), nitrogen (N), and light stress treatments on growth and development of com using both physical and molecular methods. Plant biomass, leaf area, plant height, chlorophyll content, reflectance and differential gene expression (transcriptome analysis) were measured at several growth stages. Negative impacts ofN stress on growth parameters (e.g. biomass, leaf area, etc.) were minimal ( 15-20%) through V8 compared with other stress factors that resulted in 22% or more yield loss. For example, competition with canola reduced almost 50% of com biomass and leaf area, and almost 20% of chlorophyll content at the V6 stage. Com with either canola or velvetleaf stress remaining until the V6 stage was >30% shorter than control plants. When canola stress was removed at V4, yield loss was 8% compared with 15% when stressed through V8 and were similar to shade stress. From V2-V 12, velvetleaf stress reduced biomass and ranged from 3 7-67%, whereas leaf area was 60% less than the control. Maximum com yield loss from velvetleaf stress was 33% when not controlled until V8. Shade stress reduced 60% of com biomass, 50% of the leaf area, and was 44% shorter at V2. Com biomass and leaf area progressively reduced up to 70% at V8 stage and was 20-23% shorter in shade stressed com. Cano la stress reduced 52% of the com biomass and 45% of the leaf area at V8. Similarly, velvetleaf stress reduced 60% of the com biomass and 51 % of the leaf area at V8. Interestingly, com grown in the presence of a red tarp to demonstrate low R:FR ratio, exhibited the typical shade avoidance responses for all the measured growth stages but the com under weed stress did not. Yield from the red tarp treatment was 5% higher compared with the control. Gene set enrichment analysis indicated photosynthetic processes were down regulated if weeds were present during the CWFP. Examples of the genes that were preferentially down-regulated as early as V2 were Rubisco, and Pepe. This photosynthetic gene expression remained down-regulated even if weeds were removed after the CWFP. These data indicate that weed stress permanently limits photosynthetic capabilities even after removal and may be one of the most important factors contributing to end-of-season yield loss.

Library of Congress Subject Headings

Corn -- Growth

Corn -- Yields

Corn -- Weed control

Format

application/pdf

Number of Pages

158

Publisher

South Dakota State University

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