Biotechnology, Breeding and Seed Systems

A technology, already released to seed companies along with specially bred IR maize hybrids, inbreds and OPVs, for seed treating maize with minuscule amounts of herbicide, providing season long Striga control.
Five IR maize hybrids nominated to the national performance trials (NPT), the release procedure in Kenya.
Over 188 farmers participated in testing the IR maize material and assisting us in its evaluation. They and their neighbors have provided the feedback necessary for us, the seed companies and herbicide producers, and the regulators that the products are ready for bulking up and commercial scale evaluation in areas where Striga infestation is most severe – areas where the yields are more than doubled when this technology is used.
The progress and success of this Rockefeller project has been brought to the attention of the international scientific community, to the farmer community, and to the general public by, brochures and other publications, press releases, presentations at conferences, and through meetings with chemical companies, seed companies and regulators.
Trained an MSc. student.

B. Key results from the University of Sheffield

1. Resistance to Striga in wild relatives of maize

Novel sources of resistance to Striga hermonthica were observed in a wild relative of maize, Tripsacum dactyloides. S. hermonthica development was arrested after attachment to T. dactyloides. Histological analysis demonstrated poor haustorial differentiation on T. dactyloides compared with Z. mays
Results suggested that T. dactyloides produced a signal that inhibited haustorial development.
Partial resistance to infection was inherited in a Z. mays –T. dactyloides hybrid.

2. Resistance to Striga in Transposon-tagged maize

Laboratory screens demonstrated S. hermonthica development was impaired on one transposon-tagged maize line (3689): these attached parasites did not emerge above ground.
Parasite development was inhibited post attachment indicating an incompatibility between host and parasite.
No reproduction (hence seed production) of S. hermonthica was possible on this line.

C. Key Results from Applied Biotechnology Center (ABC) - Mexico

1. Wild relatives

Analysis of the performance of a 38 chromosome hybrid (18 Tripsacum and 20 maize) and a 28-chromosome hybrid (18 Tripsacum and 10 maize) showed no dosage dependent relationship between the performance of a hybrid and the composition of maize in the genome when plants contained 15 or more Tripsacum chromosomes.
All lines derived sexually from plants with 24 or less chromosomes displayed no tolerance to Striga their growth being significantly lowered under Striga infestation. Transfer of the Striga tolerant trait from Tripsacum to maize may not be achieved by conventional wide cross techniques.
Elucidation being done on genetic bases of tolerance in Tripsacum, identification of differences in the transcriptome, proteome and metabalomes of Tripsacum and maize under infection by Striga.
Libraries (cDNA) from the roots of uninfected Tripsacum and maize and two hybrids have been generated and we plan to generate libraries from Striga-infected roots in the near future. These libraries will be used in a modified differential subtraction chain approach to identify those genes differentially expressed between the experimental systems.
A collaboration with the Institut de Recherché pour le Development (IRD) in Montpellier, France allowed the preliminary analysis of the proteomes of the roots of a 38 chromosome Maize-Tripsacum hybrid and maize under both Striga-infected and uninfected conditions. Analysis of 2D gels indicates that there are differences between the proteomes of maize and the maize-Tripsacum hybrid before and after Striga infection and that there is some differential response of both maize and the hybrid to Striga infection.

2. Transposon-tagged Maize

In total, 23 of the F2 entries were selected after the rounds of screening as having heritable field level tolerance to Striga. Some of these lines have been selfed up to F7.
Two lines, 252-B and 3689-B performed better under Striga infestation than uninfected plants. Field evaluations had deemed line 252-B as tolerant to Striga (some plants had emerged Striga but their performance was not noticeably impeded) while 3689-B was resistant (no Striga emergence). The first observation from the pot study was that the Striga plants growing on the 3689-B lines did not emerge from the growth medium while those on H511 did.
The lack of Striga emergence from the soil coupled with the apparent tolerance of 3689-B to infection by Striga make this line a very interesting and important genetic resource for Striga control strategies.
In 2001, remnant seed from the 23 selected F2 lines were grown in the field in Mexico. Each plant was selfed and DNA was isolated. The resulting F3 seed was sent to Kenya and a large-scale field screen was conducted in Alupe in the short rains 2002. The DNA isolated from the F2 entries was used to construct a linkage map; the map for 3689-B is complete.