Plant improvement – start clean, end clean

Hugh Campbell, Hortgro technical and plant improvement manager shares some of the most pertinent questions about plant improvement and its necessity for sustainable growth.

What is plant improvement?

Plant improvement is a continuous process that aims to produce better fruit trees.  New and improved genetics is one of the cornerstones of plant improvement. New cultivars provide better yields, colour, texture, storability etc.  Plants are also improved by removing economically important pests and diseases.  A plant improvement scheme’s main focus is to ensure that plant material is free of economically important viruses.

What is the value of plant improvement and a certification scheme to the grower?

“The success of the grower starts with good plant material (trees). They must be very sure that they get the right variety – and properly selected material of that variety – on the correct rootstock. And the material must be free not only of quarantine pathogens but also free of viruses and internal diseases that will harm fruit yields and quality.” Quote by John van Ruiten – Director of Naktuinbouw, the Netherlands Inspection Services for Horticulture.

There is no cure or spray for a virus or viroid.  Your only option is to remove and destroy a virus or viroid infected tree.  A virus is like a parasite.  It does not kill your tree as it uses the cellular machinery of the tree to produce more viruses.  Your only way of managing viruses is to ensure that you don’t have them in your trees before you plant your trees.

• Viruses are spread through propagation material – i.e. if you cut budwood from an infected tree you will spread it to all the trees made from that budwood.
• Viruses reduce your bud-take.
• Economically important viruses can reduce tree growth and yield by 10 -40% depending on the virus.
• Viruses can reduce tree survival and increase management costs.

Start clean, end clean.  The plant certification scheme is designed to provide planting material that has been tested to be clear of selected economically important viruses. Uncertified plant material requires that the trees be visually clean.  You cannot easily see viruses on planting material. No virus tests are required for uncertified planting material.

How is plant improvement and certification managed in the South African deciduous fruit industry?

In the context of plant improvement, certification is the process of providing growers with evidence that plant material of official varieties has been tested and certified for trueness to type (i.e a Kakamas is a Kakamas), health status (free of scheme viruses etc) and physical quality (size, thickness etc).

The Deciduous Fruit Plant Improvement Association (DPA) or Sagtevrugteplantverbeteringsvereniging (SPV) is the delegated authority for plant improvement for stone and pome fruit in terms of the Plant Improvement Act 53 of 1976.

PlantSA is a non-profit company that manages the voluntary certification scheme for deciduous fruit (DPA) and grapevines (VIA).

Only registered plant improvement organisations (PIO’s) may apply for the certification of propagation material.

The classic approach for plant improvement of ‘start clean – end clean’ is to start with a nucleus plant that is placed in a bio-secure facility that is tested clean and kept clean through regular inspection and testing.  Plant material from the nucleus plant is used to make foundation plants. These foundation plants are used to provide material for mother plants which are ideally placed in bud parks but currently are mostly in commercial orchards.  The mother plants are inspected and regularly tested and are used to cut budwood that is provided to the registered nurseries to make nursery trees.

PlantSA oversees inspects and audits this process throughout the year (spring, summer, autumn, and winter) providing a certified blue label for plant material that meets the requirements of the scheme.

The inspection of uncertified plant material is a DALRRD (Dept of Agriculture Land Reform and Rural Development) function.  The DPA can refuse to certify trees but only DALRRD has the power to prohibit the sale of non-compliant trees.  Currently, DALRRD has a capacity challenge and cannot fully meet this mandate.

What is the difference between the Deciduous Fruit Plant Improvement Association (DPA) and a Plant Improvement Organization (PIO)?

The DPA is the authorised authority that manages and inspects certified material. They therefore have an oversight role.

There are currently three PIO’s (SAPO, Topfruit and Stargrow) that operate under the DPA.

The role of a PIO is to import, breed or select new or improved cultivars or clones.  Currently, only PIO’s may apply for certification of plant material.  The PIO’s are responsible for the multiplication of the certified plant material (buds) that they then provide to registered nurseries – who then make the trees.

How does a nursery fit into the process?

“Usually, when we speak about good quality, we speak about how the tree looks, but that is something that our clients can check – they cannot check the inside.  And it’s the thing that you cannot see that you must trust, that may give you the problem in the future.  So that is what Naktuinbouw must guarantee, and why I think certification is necessary.” Quote by Dutch nurseryman Han Fleuren relating to the Dutch certification scheme managed by Naktuinbouw.

In SA only registered nurseries may produce and sell certified trees. The need of the nursery is to have access to clean, high-quality budwood and rootstocks.