Development of Fusarium in Cotton Bolls: Greenhouse and Field Results Breno Leite, David Wright, Jim Marois & Daniel Mailhot University of Florida, Quincy, FL Development of Fusarium in Cotton Bolls: Greenhouse and Field Results Breno Leite, David Wright, Jim Marois & Daniel Mailhot University of Florida, Quincy, FL Beltwide Cotton Conferences, 2007

HealthyHardlocked Open Cotton Bolls Locks fail to allow fiber outward expansion Do not fluff out Beltwide Cotton Conferences, 2007

Hardlock causes yield losses ranging from % Harvested Rows Beltwide Cotton Conferences, 2007

Associated with infection by Fusarium verticillioides through the flowers Most severe along Gulf Coast and is a major limiting factor of Florida cotton yield Flower thrips and bumblebees are likely to be contributing factors for infection and Fusarium dispersal (will be discussed in another presentation*) *3:30 PM 01/11/07 Relationship Between Flower Visitors and Cotton Hardlock, B. Leite, J. Marois, D. Wright, E. Osekre and D. J. Mailhot Hardlock Beltwide Cotton Conferences, 2007

Mature cotton flower. The cotton flower contains both male and female parts. Development of the bud from match head square to flower Illustrations Source: Cooperative Extension Service, University of Georgia College of Agricultural and Environmental Sciences Beltwide Cotton Conferences, 2007

Illustrations Source: Cooperative Extension Service, University of Georgia College of Agricultural and Environmental Sciences Fusarium conidia

Beltwide Cotton Conferences, 2007

* Hardlock of cotton seriously affects yield in many areas of the southeastern United States, and can be devastating in the panhandle of Florida. * In 2002 it caused over $20,000,000 in lost yield, reducing Florida’s average yield from 650 lb/acre to less than 400 lb/acre. * Hardlock is more severe when there is: High nitrogen High plant density Insect damage Seed rot High temperature and humidity (?) Cool nights (Dan Mailhot*) * = PhD thesis – University of Florida

Beltwide Cotton Conferences, 2007 General: Characterize the causal agent of the disease and to develop effective control measures against the disease. Specific: Find the principles of disease establishment. Follow step by step the pathway of Fusarium conidia germination. Find out why some control measures fail or failed in past years. Our Objective:

Beltwide Cotton Conferences Traditional boll rots. Boll rots usually are the product of insect damage or pathogen activity after the bolls have opened or early in the season when the carpel turns brown or black and never opens. Boll rots occur during wet weather when the cotton boll or fiber is colonized by a number of pathogens, although only a few fungi are responsible for the majority of infections. These include Alternaria gossypina (Thuem.) Hopkins, Curvularia spp., Diplodia gossypina Cke., Helmithosporium gossypii Tucker, Fusarium spp., and Phomopsis.

Beltwide Cotton Conferences, 2007 Thus far we have shown that the majority of hardlock is caused by the fungal pathogen Fusarium verticillioides, also known as F. moniliforme. This is the same organism that causes corn ear rot. We have shown that the main mode of infection is through the cotton flowers, and that fungicides applied to the flowers will control the disease. This is an entirely new approach to the etiology and control of the disease and in 2003 field plots are replicated throughout the southeastern states in an attempt to reproduce the results developed at the NFREC at Quincy. This has become a regional project with university faculty from Louisiana, Mississippi, Alabama, Georgia, South Carolina and Florida (NFREC and WFREC) working together, with major funding provided by Cotton Incorporated.

Beltwide Cotton Conferences, 2007 Image analysis (Software Image J – NIH) to estimate fiber density in a determined area. Device designed to facilitate fiber count per area (A). Typical healthy fiber density (B). Typical hardlock fiber density - type 4. Close view suggests that there is debris deposited in between the fibers (C). A healthy cottonseed (H) with a diseased cottonseed, hardlock – type 4 (D).

Beltwide Cotton Conferences, 2007 Relationship between density (% fiber per area) and cottonseed weight. Healthier locks consistently exhibit higher seed weight and less fiber density (ideal for picking). In contrast, seeds from bolls with hardlock (type 3 and 4) have lower weight and high fiber density (not harvestable).

Beltwide Cotton Conferences, 2007 Detection of Fusarium- like structures (hyphae and macroconidia) associated with hardlock of cotton. Structures, hyphae (A, C, D) and macroconidia (E, F) were observed in between the lines demarked above (B). Notice the yellow- brown coloration.

Beltwide Cotton Conferences, 2007 Average temperature from 00:00 to 06:00 and hardlock severity

Beltwide Cotton Conferences, 2007

Conclusions Mean temperature from 00:00 to 06:00 negatively associated with hardlock severity Relationship strongest between 21 and 25ºC Predictions typically within 20% of observed hardlock for day

Beltwide Cotton Conferences, 2007 Average daily temperature (TEMP) and average relative humidity (RH) at Jay, FL. The information for these graphs was obtained from the Florida Automated Weather Network (FAWN – Preliminary work revealed that differences between Quincy and Jay, FL, were found mainly during June and July of In the beginning of June RH in Jay was approximately 10 units lower than Quincy (A). These differences decreased during the next 60 days. RH was still low when bloom started in July. In contrast, temperature was slightly higher throughout the same period (B).