Relationships of pre-inoculation high temperature to root browning caused by Pythium aphanidermatum in hydroponically-grown sweet pepper

Abstract

Episodes of high root-zone temperature (33ºC) were investigated in relation to susceptibility of sweet pepper to root rot caused by Pythium aphanidermatum. Pepper plants were grown in aerated nutrient solution in hydroponic units positioned in temperature-controlled water baths. Root zone temperature was 23ºC except during high temperature treatments. Roots were exposed to 33ºC for 0 to 216 h, inoculated with P. aphanidermatum and assesseda at intervals for colonization by the pathogen and for severity of browning (necrosis). The pathogen colonized all roots within 12 h following inoculation. The roots turned brown earlier when exposed to 33ºC for more than 9 h prior to inoculation compared to those exposed for 0 to 6 h. Browning developed progressively earlier as the period at 33ºC was increased from 9 to 144 h, and was 4 days earlier for exposures of 144 to 216 h compared to 0 to 9 h. Browning was precocious also when inoculation was delayed as long as 216 h following exposure at 33ºC for 72 h. We conclude that high temperature predisposes pepper plants to precocious browning caused by P. aphanidermatum and that predisposition lasts for at least 9 days. Keywords: Capsicum annuum, predisposition, stress, root rot. RESUMO Relações entre elevadas temperaturas na pré-inoculação e o escurecimento radicular causado por Pythium aphanidermatum em pimentão hidropônicoEpisódios de elevada temperatura na zona radicular foram analisados em relação à suscetibilidade de pimentão à podridão radicular causada por Pythium aphanidermatum. As plantas foram cultivadas em solução nutritiva aerada em unidades hidropônicas contidas em caixas com controle da temperatura. A temperatura da zona radicular foi de 23ºC, com exceção dos períodos dos tratamentos com elevada temperatura. As raízes foram expostas a 33ºC por 0 a 216 h, inoculadas com P. aphanidermatum e avaliadas quanto à colonização do patógeno e a severidade do escurecimento (necrose). O patógeno colonizou todas as raízes em 12 h. As raízes escureceram precocemente quando expostas a 33ºC por mais de 9 h, quando comparadas com raízes expostas por 0 a 6 h. O desenvolvimento de escurecimento precoce foi progressivo quando o período a 33ºC aumentou de 9 para 144 h e ocorreu quatro dias antes quando as raízes foram submetidas a temperatura elevada de 144 a 216 h, quando comparadas com 0 a 9 h. O escurecimento precoce também ocorreu quando a inoculação foi realizada por até 216 h após a exposição a 33ºC por 72 h. Conclui-se que elevadas temperaturas predispõem plantas de pimentão ao precoce escurecimento radicular causado por P. aphanidermatum e que a predisposição se mantém por um período mínimo de nove dias. Palavras-chave: Capsicum annuum, prédisposição, estresse, podridão radicular, hidroponia.

Quantitative relationships of Pseudomonas chlororaphis 63-28 to Pythium root rot and growth in hydroponic peppers

“…28 to 34˚C) (Sutton et al, 2006). Sopher & Sutton (2009) confirmed that high root-zone temperature favors rapid development of root rot and found that roots of healthy peppers were predisposed to early and severe root browning when exposed to 33˚C for nine to 144 h and subsequently inoculated with P. aphanidermatum.…”

“…Cubico (De Ruiter Seeds Inc., Columbus, OH, USA) were grown on a bench in a growth room as described by Sopher & Sutton (2009). In brief, 5-week old seedlings in rock wool plugs (2.5 cm X 2.5 cm X 4.0 cm; Grodan, Roermond, The Netherlands) were placed in 5-cm diameter mesh pots and transferred to single-plant hydroponic units.…”

“…The hydroponic units were placed in temperaturecontrolled water baths to control root zone temperature as described by Sopher & Sutton (2009). The baths were positioned on the bench in the growth room.…”

“…The protocols used for maintenance and growth of P. aphanidermatum and for inoculating pepper roots were described by Sopher & Sutton (2009). In summary, the pathogen was maintained on root tissue, re-isolated on a Pythium-selective agar medium, and induced to sporulate in Petri dishes containing V8 agar medium.…”

“…Taken together, the reports suggest that P. chlororaphis 63-28 justifies further investigation for dual activity as an inoculant to enhance productivity of pepper crops in which little or no disease is present and as an agent to suppress Pythium root rot. Findings that high root zone temperature predisposes pepper plants to Pythium root rot (Sopher & Sutton, 2009) underscore the need to examine effectiveness of treatments in predisposed as well as non-predisposed plants.…”