Effect of plant extracts on radial growth of Helminthosporium oryzae causative of Brown spot disease of rice under in-vitro

Brown spot disease, caused by Helminthosporium oryzae, is worldwide problem capable of causing considerable damage to paddy in the nursery, field or grain yield. The disease is seed borne, and thus can be transmitted through infected seeds and crop residues, alternate hosts and contaminated irrigation water. The objective of this study was to evaluate the effect of plant extracts on radial growth of Helminthosporium oryzae on rice plants. An in-vitro experiment was conducted at the Plant Pathology Laboratory of National Root Crop Research Institute, Umudike, Abia State, in Nigeria. Treatments included water and alcohol extracts of Azardiractha indica (Neem leaves), Piper guinensis (seeds), Garcinia cola (Bitter cola seeds), Ocimum gratissimum (leaf) and Vernonia amygdalina (leaf); and synthetic fungicide (Benomyl) at a concentrations of 10, 25 and 30% of the extract applied to H. oryzae in culture. The test materials were administered on Helminthosporium oryzae, sourced from rice seeds and infected shoot system of rice. Alcohol extract of Piper guineensis had the highest radial growth inhibition (89.89%) by the fifth day, but was not significantly different from Azardiractha indica, which had an inhibition value of 81.02%. The least effective plant extract was Ocimum gratssimum with radial inhibition of 11.50%, which occurred also on the fifth day. Plant extracts were as effective as the synthetic fungicide in inhibiting growth of the test fungus. Therefore, the effective extracts, all of which are readily available to the farmers, should be promoted instead of the synthetic fungicides, which are in limited supply and invariably expensive for rice farmers in Nigeria.La maladie des taches brunes, caus\ue9e par Helminthosporium oryzae , est un probl\ue8me mondial susceptible de causer des dommages consid\ue9rables au riz en p\ue9pini\ue8re, champ et en rendement en grains. La maladie est transmise par les semences et peut donc \ueatre transmise par des semences et des r\ue9sidus de culture infect\ue9s, des h\uf4tes alternatifs et de l\u2019eau d\u2019irrigation contamin\ue9e. L\u2019objectif de cette \ue9tude \ue9tait d\u2019\ue9valuer l\u2019effet d\u2019extraits de plantes sur la croissance radiale d\u2019Helminthosporium oryzae sur les plants de riz. Une exp\ue9rience in vitro a \ue9t\ue9 men\ue9e au laboratoire de phytopathologie de l\u2019Institut national de recherche sur les cultures racines, Umudike, \uc9tat d\u2019Abia, au Nig\ue9ria. Les traitements comprenaient des extraits aqueux et alcooliques d\u2019 Azardiractha indica (feuilles de Neem), de Piper guinensis (graines), de Garcinia cola (graines de cola amer), d\u2019 Ocimum gratissimum (feuille) et de Vernonia amygdalina (feuille); et fongicide synth\ue9tique (Benomyl) \ue0 des concentrations de 10, 25 et 30% de l\u2019extrait appliqu\ue9 sur H. oryzae en culture. Les mat\ue9riaux d\u2019essai ont \ue9t\ue9 administr\ue9s sur Helminthosporium oryzae, provenant de graines de riz et d\u2019un syst\ue8me de pousses de riz infect\ue9. L\u2019extrait alcoolique de Piper guineensis avait l\u2019inhibition de la croissance radiale la plus \ue9lev\ue9e (89,89%) au cinqui\ue8me jour, mais n\u2019\ue9tait pas significativement diff\ue9rente de celle d\u2019Azardiractha indica, qui avait une valeur d\u2019inhibition de 81,02%. L\u2019extrait de plante le moins efficace \ue9tait Ocimum gratssimum avec une inhibition radiale de 11,50%, qui s\u2019est \ue9galement produite le cinqui\ue8me jour. Les extraits v\ue9g\ue9taux \ue9taient aussi efficaces que le fongicide synth\ue9tique pour inhiber la croissance du champignon d\u2019essai. Par cons\ue9quent, les extraits efficaces, qui sont tous facilement disponibles pour les agriculteurs, devraient \ueatre encourag\ue9s \ue0 la place des fongicides synth\ue9tiques, qui sont en quantit\ue9 limit\ue9e et invariablement co\ufbteux pour les riziculteurs au Nigeria