Foster, Scott D.

Galea, Victor J.

Henzell, Robert G.

Herde, Damian J.

Jordan, David R.

Ryley, Malcolm J.

University of Queensland eSpace

l0
l5
20
t ],h f urv,,t^,',1'H!"J'2J co'/e-*"e 
*taqo'rc*:/t
Tuth Zez
New Genes for the Battle against Sorghum Ergot
r'2Damian J. Herde. 3David R. Jordan,sRobert G. Henzell,4Scott D. I:'osler,2Malcolm
J. Ryley and]trlictor J. Galea.
t School of Agriculture and Horticulture. Universitv of Queensland Gatton Campus. QLD 43.t3; l
Queensland Department of Primary Industries. 203 Tor St. Toor'voomba QLD -1350: sQueensland
Department of Primary Industries. Hermitage Research Station, Wam{ck QLD 4370: aQueensland
Department of Primary Industries. Centre for Tropical Agriculfure. Marceba QLD 4880.
Abstract
Sorghum ergot (Clm'iceps africana) remains a serious threat to the Australian
sorghum industry since it's discovery in 1996. This is due to ongoing toxicity issues,
narrowing of the planting window, and increased cost of hybrid seed production.
Successful pollination ("escape" resistance) is the only means of avoiding disease in
susceptible lines. Ergot resistance is reported to show quantitative inheritance with
considerable genotype-environment interaction. This paper reports on studies carried
out to establish the inheritance of ergot resistance and related traits in Fl, F2 and BCIFI
populations derived from crosses between the resistant germplasm line IS8525 and two
susceptible inbred lines (31945-2-2 and 60535-2-2) Significant levels of dominance
were obseryed for resistance. This result, combined with frequency distribution data
from the F2 and BC (data not presented), indicates the possibility of major gene action,
an unexpected but beneficial discovery. Pollen traits were also studied, with significant
dominance found towards decreased pollen viability. Despite this, ergot resistance was
undiminished, leading to the conclusion that resistance in IS8525 is a non-pollen based
mechanism, which remains to be identified.
25 Introduction
C. afi"icana is a non-systemic floral pathogen, which infects unfertilised florets,
replacing the developing ovary with a fungal mass (sphacelium). Sticky honeydew oozes
from infected spikelets, carrying spores for further infections.
IS8525 has been tested in a number of countries (Australia, South Africa and the
30 USA), and shown very high levels of ergot resistance across a range of environments
(Dahlberg et a1.,2001). Experimental work was undertaken to determine the ease of
breeding ergot resistant sorghum lines based on IS8525.
Pollen traits need consideration, as poor pollen viability or quantity will lead to poor
fertilisation and increased ergot infection (Mclaren, 1997). However, ergot resistance
35 that depends on pollen cannot be incorporated into a male sterile line for use in hybrid
seed production. Ergot studies have included close scrutiny of pollen traits to determine
whether this is the source of resistance in IS8525.
Materials and Methods
Trial design and set-up:
A generation means design was followed to produce two populations (Kearsy and
Pooni, 1996). The first population was based on IS8525 (ergot resistant), and 31945-2-
2 (ergot susceptible), while the second was based on IS8525 and 60535-2-2 (moderately
ergot susceptible). Each population consisted of two homogeneous parents, the Fl
cross between these parents, theFZ generation produced by self pollination of the Fl,
and two backcross generations @Cl and BC2) developed by crossing the Fl to each
parent. Control plots were included.
40
45
50
Panicles were artificially inoculated with a conidial suspension (1x106 conidialml) at
5Ao/o anthesis, and non-flowering spikelets removed. Pollen quantity was assessed
visually (score from 0 to 10, 0 : no pollen, 10 : abundant pollen); pollen viability (%)
was scored by staining pollen grains with A,25Yo iodine solution and assessing
microscopically; and ergot severity was visually assessed three weeks after inoculation
(% infected spikeletslpanicle).
This experiment was conducted at Hermitage Research Station, Warwick Qld There
were three planting dates, with two replications per planting date.
Analysis
A mixed model using smoothing splines (Verbyla, 1995) was fitted to each of the
three outcome variables (ergot percentage data was arcsine square root transformed
prior to analysis). These models accounted for possible flowering dats effects as well as
any possible correlations induced by repeatedly measuring the same plots (Verbyla et al.,
1999). Sorghum Line by time interactions were also considered in the mixed model.
Genetic mean parameters were estimated using the line main fixed effects calculated at
the average time.
The convention of using the susceptible line as the P1 parent (Kearsy and Pooni,
1996) has been used. Caution should be taken when interpreting the results as this will
not always be the parent with the higher phenotlpe value.
Results
As results for the two populations show similar
population (IS8525 and 31945-2-2) are displayed.
Table I displays the outcome of the Kearsy and
susceptible line is always the Pl parent (by definition)
trends, only results for the first
Pooni (1996) analysis. As
then a value of [d] which has
55
60
65
the
the70
same sign as the corresponding [a] shows dominance towards the susceptible line.
Conversely an opposite sign shows dominance by the non-susceptible line.
Table l. Estimated values for genetic mean parameters and respective p values (for
tests against zero) for the population of IS8525 and31945-2-2.
Mean Parameter Transformed o/oBrgot % Pollen Viability Pollen Quantity (0-10)
Parent Mean, m 23.73 (p<0.001) 7r.38 (p<0.001) 1.61 (p<0.001)
Additive genetic
component of means, [a] 13.35 $<0.00i) A -4.0s (p=0.003) B -0.48 (F0.006) B
Dominance genetic
component of means, [d] -11.55 {g0.002) B -25.94 0x0.001) A 1.84 {50.002) B
Dominance Ratio [d]/[al ' -0.87
Fit of Model {p value) D 0.12
6.37
0.86
-3.79
0.34
75 o Value towards 31945-2-2.
u Value towards IS8525.
"Value of 1 or -1 shows complete dominance.
DP 
value >0.05 indicates the model fits assumptions of additive and dominance gene effects.
80 The first main conclusion from Table 1 is that dominance is significant for ergot
resistance and pollen quantrty, despite the significant dominance for decreased pollen
viability. Another important conclusion is that the observed traits are explained
sufficiently by additive and dominance gene effects, pointing towards no maternal effects
or interactions between genes (epistasis).
85
4
Discussion
Additional analysis (data not presented) also reinforce the conclusion that ergot
resistance in IS8525 is a major gene effect rather than being quantitative in nature.
The strong dominance for ergot resistance will be very useful in the production of
90 sorghum hybrid seed. There need only be one parent containing resistance genes to
produce resistant hybrids.
Future work will provide predictions of ergot resistance heritability from IS8525, and
determine the mechanisms(s) responsible.
Acknowledgements
95 Seed populations used in these experiments were developed by the QDPI sorghum
breeding team at Hermitage Research Station, Warwick Queensland.
References
Dahlberg JA, Bandyopadhyay R, Rooney WL, Odvody GN, Madera-Torres P (2001)
Evaluation of sorghum germplasm used in US breeding programmes for sources of
100 sugary disease resistance. Plant Pathologt 50, 681-689.
Kearsey MJ, Pooni HS (1996) The Genetical Analysis of Quantitative Traits. (Stanley
Thornes (Publishers) Ltd: UK).
Mclaren NW (1997) Changes in pollen viability and concomitant increase in the
incidence of sorghum ergot with flowering date and implications in selection
105 for escape resistance. Jounml of Phytopathologs 145(5-6), 261-265.
Verbyla AP (1995) A Mixed Model Formulation of Smoothing Splines and Testing
Linearity in Generalized Linear Models. Research Report 95/5, Departrnent of
Stotistics, The Universily of Adelaide.
I I t -69Z' gg sc 4s gtsTg patlddy'(uorssnasrq
tiipt) seurldg Eurqloorug Eursg .{q s}ee leulpnlrEuol pu? slueuruedxg 0I I
peu8rseg 3o srs,{1tuy eq1 (OeAt) IS rueqle.A11 'CW pr€lvruex 'Ug s11lnJ '6y e1,(q:a6


New genes for the battle against sorghum ergot

http://espace.library.uq.edu.au/view/UQ:296791/UQ296791_fulltext.pdf

New genes for the battle against sorghum ergot

Abstract

Similar works

Full text

Available Versions

University of Queensland eSpace