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Oktober 2018
74
Wheat:
Breeding the future
D
uring the July 2018 issue (page 96) we introduced the pre-
breeding project being conducted at Stellenbosch Univer
sity’s Plant Breeding Laboratory (SU-PBL) as part of the
Department of Science and Technology (DST)-Grain SA
National Wheat Breeding Platform.
The aim of the project is to develop and distribute germplasm back
to all wheat breeding programmes that will assist in breeding ef
forts to achieve higher yielding wheat cultivars. The project consists
of seven work packages in order to realise this aim: Stakeholder
engagement; germplasm gathering and screening; male sterility
mediated marker assisted recurrent selection facilitated crossing
programme; molecular marker identification, optimisation and im
plementation; high throughput phenotyping; capacity building; and
seed multiplication and distribution.
This article will focus on one of the more easily relatable traits that
the project is focusing on, namely grain size and weight – traits that
are traditionally considered as part of the quality trait family. In re
cent years plant breeders have, however, been able to prove that
given the correct genetic building blocks larger seeds can also lead
to a higher total grain yield per square metre. Previously it was be
lieved that larger seeds will just give cause to less seeds per square
metre – a zero gain being implied.
Grain weight, as measured by thousand kernel weight, is largely
influenced by a kernel’s dimensions such as grain length and width.
The genetic control for grain length and
width is, however, not that easy to deter
mine, and many studies into this are on
going. Among these are notably efforts
by the International Wheat Yield Partner
ship with which this project is aligned,
together with our ARC-Small Grain
(ARC-SG) pre-breeding partner, the
Sydenham-laboratory.
Following from this collaboration
and own initiatives, the SU-PBL and
ARC-SG have been able to identify more
than two dozen potential genetic mark
ers that could aid in the selection for
larger kernel size. This will enable us
to screen large amounts of germplasm
that include local as well as international
contributions, casting the net as far as
possible in order to identify the best
genetic building blocks to add to our
South African germplasm pool.
Before using any new genetic markers
for genotyping germplasm, it needs to
be validated by phenotyping the relevant
germplasm. The problem with measur
ing a single kernel’s width and length as
well as thousand kernel weight, is that
it is time consuming and labour intensive. Repeatability of measure
ments is also a challenge.
Recent advancements in imaging technology are, however, enabling
us to establish high throughput phenotyping pipelines that are able
to measure single kernels as part of larger batches to determine
kernel width and length, and also to rapidly calculate thousand ker
nel weight at a reasonable cost per data point. High throughput phe
notyping is not just an activity performed using drones.
Several Android based applications have been developed by vari
ous international research groups over the past few years as part
of similar efforts. Reinventing the so-called wheel is therefore not
needed. The world of wheat breeding is after all a small one if you
collaborate.
SeedCounter and 1KK are the most widely used. The applications
identify length, width and area of an object (see
Figure 1
) and record
the data in a format ready to export to a spreadsheet application.
Thousand kernel weight can be ascertained by using various meth
ods, ranging from counting by hand to vibration-based counters
which are most commonly used. Again, newer technology based on
laser imaging is making assessment much easier.
Our laboratory recently acquired one of these next generation coun
ters, a Wintersteiger Seed Count S-25 plus. It can count hundreds
of seeds per minute by imaging the seed-stream running through a
On farm level
Germplasm / Wheat breeding programme
Seed
Willem Botes,
chair: Department of Genetics, Stellenbosch University and research lead:
DST-Grain SA National Wheat Breeding Platform
Part 2: Perhaps it is in the seed?
Figure 1: Image of 1KK application counting and measuring seed width, length and surface area.