Abstract
Calonectria pseudonaviculata (Cps) poses an increasing threat to boxwood, a major nursery crop and iconic landscape plant worldwide. Here, we report on a potent biocontrol agent that produces small sage green (SSG) colonies on potato dextrose agar. SSG is a bacterial strain recovered from Justin Brouwers boxwood leaves with unusual response to Cps inoculation. Water-soaked symptoms developed on leaves 2 days after inoculation then disappeared a few days later. This endophyte affected several major steps of the boxwood blight disease cycle. SSG at 107 cfu/mL lysed all conidia in mixed broth culture. SSG at 108 cfu/mL reduced blight incidence by >98% when applied one day before or 3 h after boxwood were inoculated with Cps. Its control efficacy decreased with decreasing bacterial concentration to 103 cfu/mL and increasing lead time up to 20 days. When applied on diseased leaf litter under boxwood plants, SSG reduced Cps sporulation and consequently mitigated blight incidence by 90%. SSG was identified as a new member of the Burkholderia cepacia complex with distinct characters from known clinical strains. With these protective, curative, and sanitizing properties, this Burkholderia endophyte offers great promise for sustainable blight management at production and in the landscape.
Highlights
Boxwood blight caused by Calonectria pseudonaviculata (Cps) is an economically and ecologically important disease [1,2]
Difference was observed in germination of conidia among Cell, cell-free supernatant (CFS), and potato dextrose broth (PDB) treatments (p < 0.01), but not between the two experimental runs (p = 0.19) nor among the exposure times (p = 0.23)
Abou6t 5of2%15 conidia in control wells with PDB germinated within 1 h; their germination rate increased with time, rteimaceh,inregac1h0i0n%g a1t0408%ha(tF4ig8uhre(1F)igwuirteh 1g)erwmitlhinggeargmglrineggaatigognreagnadtifounrtahnedr dfuevrtehloerpmdeevnetloinptmo ehnytpihnateo (hFyigpuhraee2(F).igIunrceo2n).trIanscto, ncotrnaisdt,iacogneirdmiaingaetremdinatataedmautcahmlouwcherloawreartea irnatwe ienllws wellisthwCitFhSCtFhSanthtahnotsheoisne cinonctoronltrwolelwlse. lNls.oNneoonfetohfetchoencidoinaidiniawinelwls ewllisthwSiSthGScSeGllscgelelrsmgienramteindaotvederotvheer4t8h-eh 4p8e-rhiopde;riinodfa;citn, tfhaecyt, wtheerye awllelryesaeldl.lSyismedil.aSricmoinlaidriacol nlyidsiisalwlayssiosbwsearsveodbsienrwveedllsinwwithelClsFwS,itbhutCtFoSa, bleustsetroeaxtleensst.erCeoxntiedniat. tChoant ihdaida nthoattbheaedn lnyostedbeheandlyanseedmhpatdy acenlle, mthpetyygceerlml, itnhaetyedgepromoirnlya,taedndpfoeowrleyr, gaenrdmfleinwgesrdgeevremlolipnegds fduervtheelorp(Fedigfuurreth2e).r (Figure 2)
Summary
Boxwood blight caused by Calonectria pseudonaviculata (Cps) is an economically and ecologically important disease [1,2] This disease was first reported in New Zealand [3] and the United Kingdom [4]. English boxwood is one of the most susceptible boxwood cultivars evaluated to date, and may be destroyed by Cps within a week of inoculation [9,10,11] This pathogen attacks several species of pachysandra [12,13,14,15], sweet box [16,17,18], and potentially some common groundcovers and boxwood companion plants outside of the Buxaceae family [19]
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