Evaluate the role of transplants and the effect of defense-inducing, growth-promoting and fertility treatments on yield and the development of onion bacterial diseases.
Pennsylvania State University
Southeast Research and Extension Center, Landisville, PA
Beth K. Gugino, Assistant Professor
Wimauma, FL 33598 Department of Plant Pathology

Objective: Determine the efficacy of single and combination product treatments, both soil and foliar, of conventional and biological fungicides to cv. ‘Candy’ onion transplants in providing disease onset control and management and promoting growth and vigor. And to explore the potentiality of PGPR (Plant Growth-Promoting Rhizobacteria) stimulated ISR (Induced Systemic Resistance) to suppress pathogenic bacteria, along with an initiated, preconditioned, SAR (Systemic Acquired Resistance) plant response to prevalent onion diseases for increased protection.
Method: Randomized, complete block design beds of cv. ‘Candy’ Onion bare root transplants were planted on 5-May at the Southeast Research and Extension Center, Landisville, PA, in spring 2011. The beds were 12ft, and implemented 4” plant spacing, 4 row width, with 4 replicates. The transplants were inoculated at a rate of 1.0 x 108 cfu/ml, with a mixed bacterial suspension of Pantoea agglomerans and P. ananatis, that were isolated from symptomatic onions in 2009 and 2010. Both gram negative bacterium, Pantoea agglomerans, which causes Leaf Blight and Bulb Rot in Onions and P. ananatis, which causes Center Rot in Onions, are among a number of bacterial disease causing pathogens that plague onion crops, damaging both leaf and bulb tissue, resulting in lower quality and yields.

Within two days of transplant, soil treatments of Myke Pro® (a Mycorrhizal Inoculant) and Companion® (a broad-spectrum, multiple-mode, biological fungicide for the prevention, control and suppression of soil-borne and foliar diseases) were administered at rates of 600g/53-gal (36 spores/150mL) and 64 fl. oz./100-gal drench respectively, around the base of each plant, via backpack sprayer to selected plots.

Foliar treatments, initiated on 22-JUN, of Actigard® 50WG (a single-mode systemic plant activator), Employ® (a single-mode plant health promoter), Kocide® 3000 (a Copper Hydroxide based fungicide/bactericide) and Penncozeb™ 75DF (a zinc ion and manganese ethylenebisdithiocarbamate fungicide) were applied in various combinations and/or independently at intervals congruent to their labeling, to selected plots.
Results: Marketable yield, weight and percentage of bacterial rot (by weight) were determined at harvest from an 8ft bed area from each plot. The bed areas were assessed visually for bacterial disease incidence and then graded by size class. The plots that were treated with Companion® and Employ® displayed 21 – 23% longer leaves than the untreated and un-inoculated controls. Combination treatments of Companion® and Actigard® as well as Myke Pro® and Employ increased foliar length by 19%.

onion_research Bacterial Rot, by weight, was least present at 10.6% in the plot treated with Companion.

onion_research The plots with highest marketable weight and number of bulbs were treated with combination treatments of Companion® and Employ®. In a preliminary greenhouse experiment, Companion® was applied as a drench and proven effective at reducing total bacterial lesion areas in onion plants inoculated with Pantoea agglomerans.

onion_research

Combination treatments of Companion® and Employ® in which the modes or mode of action involve ISR via PGPR and PR (pathogenesis-related) proteins, respectively, produced higher yields and weight in selected plots and also produced increased leaf lengths. The efficacy of the more conventional fungicides was less than that of the biological and systemic products overall.

Like the immune functions within our own bodies, plants with stronger immune response are less susceptible to disease. Products that elicit immune response functions such as ISR and enhance or mimic SAR through various elicitors and regulatory pathways can improve pathogen resistance. ISR, when potentiated by PGPR, can suppress disease through bacteria and soil-borne pathogen antagonism and also by inducing systemic resistance to both root and foliar pathogens. In natural conditions, where multiple pathogens exist, an increase in the level of basal resistance to several pathogens simultaneously, by means of induced resistance, is very beneficial.

Trademarks Statement:

Actigard® is a registered trademark of Syngenta Crop Protection, LLC, Kocide® is a registered trademark of E.I. DuPont de Nemours & Co. Inc., Penncozeb™ is a registered trademark of United Phosphorus, Inc., Employ® is a registered trademark of Plant Health Care, Inc., Myke Pro® is a registered trademark of Premier Tech, Ltd., and Companion® is a registered trademark of Growth Products, Ltd.