Development of a bioassay of tannin-free, bird-resistant sorghums for bird repellency

Thadeo Mokiti Cosma Tarimo, Purdue University

Abstract

Sorghum (Sorghum bicolor (L.) Moench) has the potential to reduce grain deficits in Sub-Saharan Africa, but it is highly vulnerable to red-billed quelea (Quelea quelea) depredation. Bird-resistant sorghum varieties, when incorporated into the current control methods, may reduce quelea damage. Farmers have traditionally selected brown sorghums containing tannins as means of reducing damage. However, high-tannin sorghums are not only less preferred by birds but also by humans. Because low-tannin sorghums are available, it is logical to shift sorghum production to low-tannin varieties. A laboratory bioassay was developed in order to characterize the repellency of Ark-3048. The objectives of this study were to: (1) develop a laboratory method for screening sorghums for bird repellency; and (2) determine if mature Ark-3048 grain: (a) is less susceptible to bird damage than the conventional low tannin sorghums; (b) has an extractable chemical and/or physical properties that cause repellency; and (c) if possible, identify and quantify the repellent compound(s). Caged sparrows (Passer domesticus) significantly preferred brown, low-tannin P-8333 grain to yellow Ark-3048. However, they preferred granules of Ark-3048 to P-8333 and BR-64 high-tannin sorghum. Quelea did not show any preference to whole grain P-8333 but preferred cracked P-8333 grain to cracked Ark-3048 grain and white, low-tannin whole grain Segaolene to whole grain Ark-3048. Both species avoided neutral material treated with Ark-3048 extract. More than 70% of sparrows fed exclusively on Ark-3048 died before end of the third week. The cause of death was starvation, emaciation, and salmonella infection. The repellent compound is extractable only with polar solvents. The extract repelled both species but the extracted residue did not. Both species preferred soaked grain of Ark-3048 to that of Segaolene and P-8333. The repellency of Ark-3048 seems to be lost on contact with water. Water possibly causes complexing of the repellent material with other grain components such as protein, as it does with tannins. These results suggest Ark-3048 has some bird repellent compound(s) that are toxic and can cause death. The compound(s) are neither tannin nor dhurrin. Physical barriers, especially hardness and size, possibly play a major role in the bird resistance of mature Ark-3048 grain.

Degree

Ph.D.

Advisors

Weeks, Purdue University.

Subject Area

Forestry|Agronomy

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