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Whitefly and whitefly-borne viruses in the tropics : Building a ... - cgiar

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order<strong>in</strong>g Ug<strong>and</strong>a (Legg, 1999). This<br />

expansion has been associated with<br />

<strong>the</strong> spread of a novel CMB variant<br />

(Harrison et al., 1997). The p<strong>and</strong>emic<br />

poses an immediate threat to cassava<br />

production <strong>in</strong> <strong>the</strong> areas of Tanzania<br />

border<strong>in</strong>g Ug<strong>and</strong>a <strong>and</strong> eventually to <strong>the</strong><br />

country as a whole. Research towards<br />

controll<strong>in</strong>g <strong>the</strong> disease is <strong>the</strong> focus of<br />

cont<strong>in</strong>u<strong>in</strong>g work by <strong>the</strong> Root <strong>and</strong><br />

Tubers Programme of <strong>the</strong> Lake Zone<br />

Agricultural Research <strong>and</strong> Development<br />

Institute (LZARDI) based at Ukiriguru,<br />

Mwanza. The <strong>in</strong>stitute is supported <strong>in</strong><br />

this effort by o<strong>the</strong>r <strong>in</strong>ternational<br />

research <strong>in</strong>stitutions <strong>and</strong> networks,<br />

<strong>in</strong>clud<strong>in</strong>g <strong>the</strong> International Institute of<br />

Tropical Agriculture-Eastern <strong>and</strong><br />

Sou<strong>the</strong>rn Africa Regional Center<br />

(IITA-ESARC), <strong>the</strong> East African Root<br />

Crops Research Network (EARRNET)<br />

<strong>and</strong> <strong>the</strong> Sou<strong>the</strong>rn African Root Crops<br />

Research Network (SARRNET). SPVD,<br />

<strong>and</strong> its effects on <strong>the</strong> production of<br />

sweetpotato, has received less attention<br />

<strong>in</strong> Tanzania. However, <strong>the</strong> disease<br />

poses a threat to <strong>the</strong> production of <strong>the</strong><br />

crop if left unchecked.<br />

Diagnostic surveys were conducted<br />

<strong>in</strong> mid-1998. Three target areas were<br />

chosen to represent <strong>the</strong> major cassava<br />

<strong>and</strong> sweetpotato grow<strong>in</strong>g areas <strong>in</strong> <strong>the</strong><br />

country: <strong>the</strong> “lake zone” (i.e., border<strong>in</strong>g<br />

Lake Victoria), which <strong>in</strong>cludes Mwanza,<br />

Sh<strong>in</strong>yanga, Mara <strong>and</strong> Kagera regions;<br />

<strong>the</strong> “sou<strong>the</strong>rn coast”, which <strong>in</strong>cludes<br />

L<strong>in</strong>di <strong>and</strong> Mtwara regions; <strong>and</strong> <strong>the</strong><br />

“nor<strong>the</strong>rn coast”, which <strong>in</strong>cludes<br />

Tanga, Dar-es-Salaam <strong>and</strong> Pwani<br />

regions (Figure 1). The study aimed at<br />

identify<strong>in</strong>g whiteflies <strong>and</strong> <strong>whitefly</strong>transmitted<br />

<strong>viruses</strong> <strong>and</strong> characteriz<strong>in</strong>g<br />

producer knowledge <strong>and</strong> responses to<br />

<strong>the</strong>se problems on cassava <strong>and</strong><br />

sweetpotato <strong>in</strong> Tanzania.<br />

62<br />

Whiteflies <strong>and</strong> <strong>Whitefly</strong>-<strong>borne</strong> Viruses <strong>in</strong> <strong>the</strong> Tropics<br />

Ug<strong>and</strong>a Lake<br />

Victoria<br />

Kagera<br />

Rw<strong>and</strong>a<br />

Mara<br />

Mwanza<br />

Burundi<br />

Sh<strong>in</strong>yanga<br />

D.R. Congo<br />

Tanzania<br />

Kenya<br />

Figure 1. Cassava- <strong>and</strong> sweetpotato-grow<strong>in</strong>g<br />

areas surveyed for <strong>whitefly</strong> <strong>in</strong>cidence<br />

<strong>in</strong> Tanzania.<br />

Increased Biological<br />

Underst<strong>and</strong><strong>in</strong>g<br />

<strong>Whitefly</strong> species <strong>and</strong><br />

abundance<br />

Tanga<br />

Dar-es-Salaam<br />

Pwani<br />

L<strong>in</strong>di<br />

Mtwara<br />

Mozambique<br />

Three <strong>whitefly</strong> species were identified<br />

on cassava: B. tabaci, B. afer (Priesner<br />

<strong>and</strong> Hosny) <strong>and</strong> Trialeurodes ric<strong>in</strong>i<br />

(Misra). Only B. tabaci <strong>and</strong> B. afer were<br />

identified on sweetpotato. Of<br />

303 <strong>whitefly</strong> samples collected on<br />

cassava, 175 were B. tabaci,<br />

127 B. afer <strong>and</strong> one T. ric<strong>in</strong>i. The<br />

105 <strong>whitefly</strong> samples from sweetpotato<br />

comprised 89 B. tabaci <strong>and</strong> 16 B. afer.<br />

The species B. tabaci <strong>and</strong> B. afer were<br />

found <strong>in</strong> all three survey areas. B. afer<br />

was more common on cassava than on<br />

sweetpotato. It comprised 26% of <strong>the</strong><br />

whiteflies <strong>in</strong> samples collected on<br />

cassava <strong>and</strong> 9% of those on<br />

sweetpotato from <strong>the</strong> lake zone, 53%<br />

on cassava <strong>and</strong> 11% on sweetpotato<br />

from <strong>the</strong> sou<strong>the</strong>rn coast, <strong>and</strong> 45% on<br />

cassava <strong>and</strong> 27% on sweetpotato from<br />

<strong>the</strong> nor<strong>the</strong>rn coast (see also Figure 2,<br />

Chapter 1.14, this volume).

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