Abstract
Tagosodes orizicolus is one of the main plagues of rice in tropical America causing two types of damages, the direct one, feeding and oviposition effect, and an indirect one, by the transmission of the "Rice hoja blanca virus". During 2006-2007 we carried out research under greenhouse conditions at Fundaci6n Danac, Venezuela, in order to determine the mechanisms of antixenosis, antibiosis and tolerance to T. orizicolus, which could be acting in commercial varieties and advanced lines of the rice genetic breeding programs of INIA and Fundaci6n Danac. The method of free feeding was used for the antixenosis evaluation, whereas the method of forced feeding was used for antibiosis evaluation (effect on survival and oviposition). Additionally, we used the indirect method based on biomass depression to estimate the tolerance. Some of the evaluated traits included: grade of damage, number of insects settling on rice plants, percentage of sogata mortality at the mature state, number of eggs in the leaf midrib and an index of tolerance. The results showed that rice genotypes possess different combinations of resistance mechanisms, as well as different grades of reactions. The susceptible control 'Bluebonnet 50' was consistently susceptible across experiments and the resistant control 'Makalioka' had high antixenosis and high antibiosis based on survival and oviposition. The rest of the genotypes presented lower or higher degrees of antixenosis and antibiosis for survival and oviposition. The genotype 'FD0241-M-17-6-1-1-1-1' was identified with possible tolerance to the direct damage of sogata.
Highlights
Rice in tropical America is affected by the planthopper Tagosodes orizicolus (Muir) (Common name: sogata) causing direct damage when the nymphs and adults feed from the mesophyll and phloem sap at different stages of plant development; or when the adults oviposit on the plant leaves (Zeigler et al 1994)
An indirect damage can be caused by sogata as vector of the Rice hoja blanca virus (RHBV), which is one the most important disease caused by this pest (Vivas et al 2002), reducing over 40% of rice production in Venezuela since its appearance (Malaguti 1956)
There are few references related to freechoice feeding using circle arrangements in rice exposed to T. orizicolus; the number of settling insect expressed as percentage at 24, 36 and 72h were similar to those reported by Calvert et al (2004), where ‘Fedearroz 50’ and ‘Makalioka’ were consistently less preferred by sogata
Summary
Rice in tropical America is affected by the planthopper Tagosodes orizicolus (Muir) (Common name: sogata) causing direct damage when the nymphs and adults feed from the mesophyll and phloem sap at different stages of plant development; or when the adults oviposit on the plant leaves (Zeigler et al 1994). The nymphs are whitish in color and their size varies between 0.65-0.60mm long x 0.20-0.30mm wide. As they grow, the sharpness of the lateral lines of their body increases (Meneses et al 2001). Other researchers recognized the behavior of insects associated with non-preference, the category called antixenosis has been widely accepted (Panda & Khush 1995). Each one of these three main categories of plant resistance may act by different mechanisms. Rice breeding programs have focused into obtaining new cultivars with increased resistance to direct and indirect damage produced by the insect. It have been used resistance sources that present the antibiosis mechanism, which is undesirable because sogata is able to overcome resistant in few generations (Pantoja et al 1993, Pantoja et al 1997)
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