Priority fruit and nut crops are banana, mango, passion fruit, papaya, avocado and macadamia.  Priority vegetables include Brassica, tomato, onion, French bean, snow pea, sugar snaps, Indigenous leafy vegetables commonly known as African leafy vegetables (ALVs), Asian vegetables, medicinal and aromatic plants.  Floriculture research focuses mainly on summer flowers targeting the smallholder growers including arabicum, gladiolus, lilies, (oriental, Asiatic and Easter lilies) alstroemeria, gerbera, anthuriums, eryngium and mobydick.  These projects are implemented in collaboration with strategic partners such as non governmental organizations (NGO), community based organizations (CBO), Ministry of Agriculture (MoA), FPEAK, KHDP, Horticultural Crops Development Authority (HCDA), Kenya Plant Health Inspectorate Services (KEPHIS), Jomo Kenyatta University Agriculture Technology (JKUAT) and farmers amongst others. The horticultural research in the centre is addressed within the following sub-programme.

1. Vegetable Research
The vegetable research programme has been reorganized into five sub-commodity units including Exotic Vegetables, Indigenous (African Traditional) vegetables, Asian vegetables, Medicinal and Aromatic plants and Emerging vegetables. The priority vegetable crops include Brassicas, tomato, onion, French and runner beans, snow/snap peas, indigenous vegetables, a range of Asian vegetables, medicinal and aromatic plants ([MAPS]-vanilla, aloe vera, Centella asiatia, grain amaranth, mints and garlic) and mushroom. The major constraints to vegetable production include lack of superior varieties, inadequate or poor quality seed, diseases and insect pests, inappropriate agronomic practices, poor pre-and-postharvest handling and poor marketing channels and infrastructure. These constraints are addressed using commodity value chain and stakeholder participatory approach.

2. Fruit Research
The fruit research programme has three sub-commodity units including Tropical fruits, Temperate fruits and Underutilized fruits. This programme addresses the development of superior genotypes of various fruits through introduction, evaluation, breeding and selection. The priority fruit crops are banana, mango, passion fruit, avocado, pawpaw, apples and grapes. The major constraints identified in 2005 priority setting include diseases and insect pests, inadequate knowledge on field management and poor pre-and-postharvest handling. To address these constraints, the centre is conducting several projects which include development of passionfruit varieties resistant to major diseases, introduction of superior pawpaw cultivars, capacity building of mango farmers groups on value addition and use of growth regulators to enhance grapes production.

3. Floriculture Research
The floriculture research programme has three sub units including Native Ornamentals, Exotic Flowers and Flower Propagation. This programme identifies, collects and maintains unique ornamental plant germplasm with potential for commercialization; introduction and evaluation of new varieties of popular exotic summer flowers and plant propagation technologies for the newly introduced and/or domesticated plants and potted plants. Commercialization of the superior gladiolus, gerbera, lilies (Asiatic, Oriental and Easter), zinnia, stachys and gomphrena varieties was done through on-farm demonstrations, farmer field Schools (FFS) and field days.  Mobydick and arabicum are the most popular flowers for small-scale producers in Kiambu, Nyandarua, Meru and Embu districts.  Major production constraints include poor agronomic practices, inadequate pests’ management practices and pre-and-postharvest handling skills.

4. Macadamia Research
The macadamia research sub-programme has three research units including breeding, agronomy and crop protection. Constraints to production include macadamia stink bug (Bathycoelia distincta), low soil fertility and trunk canker (Phytophthora cinamomi) and lack of suitable varieties for semi-arid areas. Breeding work focuses on development of superior varieties through introduction and selection, evaluation of cross-bred lines and local adaptation trials in the various agro-ecological zones. Development of a micro-propagation protocol for rapid seedling production is on going. Laboratory rearing of the Southern green stinkbug Nezara viridula the host insect for parasitoids of the Macadamia stinkbug Bathycoelia distincta was initiated to develop biopestides for control of this pest.

5. Dry Bean Research
In addition to the horticultural programme, the centre has been conducting research on dry beans since the initiation of the Dutch Grain Legume Project in the late 1970’s.  From the last reporting period, the following has been achieved through competitive grants. A Project titled ‘Nutribean: Improving food security and quality for low input farmers in the East African Highlands”, commenced in July 2006.  The overall project objective is to improve food security and income generation of rural people, especially women and children, in the Eastern African Highlands by sustainable bean management, and to improve local capacity for bean research and implementation of new technologies.  The specific objective is to identify parameters in bean production and cropping systems maximizing BNF, food quality and quantity under low soil fertility conditions. The five-year duration project is funded by Flemish Interuniversity Council (VLIR) and has collaborators from the University of Nairobi, KARI-Embu, INERA-Mulungu (DRC), NARO-Namulonge (Uganda), and KULeuven, Belgium.

6. Socio-Economics and Biometrics Research
This section generates and provides scientists appropriate socio-economic information and biometrics inputs required for successful project implementation. Activities include monitoring and evaluation to determine economic viability, social acceptability and market responsiveness of technologies; facilitate priority setting (ex-ante impact assessment) to identify and prioritize areas of intervention in projects and programmes; assess adoption and impact of released technologies at different stages of technology generation-adaptation-adoption- wider usage (up scaling) continuum and provide biometric support during development and dissemination of technologies, focusing on experimental design and surveys, data analysis and interpretation.

7. Business Development Section (BDS)
Commercialization of research activities was initiated in 2000 by KARI management under ARIS coordination with a focus of developing profitable and self-sustainable commercial enterprises. At KARI-Thika this unit has been restructured to a Business Development Section (BDS) which encompasses five units i.e. KARI Seed Unit; Analytical Laboratory; Farm Management Unit; Catering and Hospitality; Advisory, Training and Contract Research Unit.

7.1 KARI Seed Unit
The goal of KARI Seed Unit (KSU) is to meet farmers demand for sustainable and reliable supply of high quality seed and vegetatively propagated and open pollinated planting materials. The unit maintains all pre-released and released varieties, inbred lines and population as well as producing breeder, pre-basic and basic seeds. The formal seed sector purchases breeders seeds and informal sector purchases basic seed for further multiplication. Seed companies using breeders or basic seed purchased from KSU produce certified seed/stocks/seedlings. KSU also multiplies quality seed and planting material for sale directly to the farmers through selected seed growers/nursery operators.

7.2 Catering and Hospitality
Catering unit provides professional services and generates revenue for KARI-Thika while playing a role in public relations.

7.3 Advisory, Training and Contract Research Unit
This section focuses on the stakeholder on business related issues. It contributes to revenue generation through student attachment, farmer group capacity building, contract research and consultancy services. It contributes to marketing products and services of the centre in Hortfair shows, the Nairobi Internal Show and other provincial shows.

8 Information Management and Communications Technology Section
The section was established to create, exploit and maintain Information Technology and Communications infrastructural resources to support development and dissemination of horticultural technologies and information in KARI. The section provides support services to the centre in the area of information management and communications technology hence enabling the cnetre to achieve the overall objective. There are four units in this section i.e., Library and Information Services, Information Technology, Publications and Telephone Exchange Unit.