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61

MUTANT

COLLECTION STRAIN

HOST(S) TESTED

ISOLATES

PHENOTYPICALLY

ALTERED ISOLATES

GENES RESPONDING

TO TREATMENT

A. tumefaciens

-

mutagenesis

M. oryzae

KJ201

Rice

21 070

2,6%

203

M. oryzae

Guy11

Barley cv. Golden Promise

and rice cv. CO-39

5 248

0,1%

1

Bidirectional-

genetics

M. oryzae

KJ201

Rice cv. Nakdongbyeo

1 139

11,2%

3

Targeted gene

deletion

M. oryzae

Ina72

Barley cv. Nigrate and rice cv.

Shin No. 2

78

1,2%

1

F. graminearum

Z3643

Not tested on host plant

127

32%

40

Plasmid-mediated

integration

F. graminearum

PH-1 Wheat cv. Bobwhite

1 170

0,6%

146

F. graminearum

PH-1 Wheat cv. Bobwhite

650

1,2%

456

Transcription

factor

F. graminearum

3639 Not tested on host plant

657

25,8%

170

M. oryzae

70-15

Barley and rice cv. CO39

104

58,6%

61

M. oryzae

70-15

Barley and rice cv. CO39

47

97%

46

TABLE 1: MUTANT COLLECTIONS IN

F. GRAMINEARUM

AND

M. ORYZAE

.

mechanisms used by fungi to infect their host plants. As a result of

these large-scale genetic studies, numerous genes have been as-

signed roles in the biological processes of fungal pathogens.

Owing to the importance of these genetic resources, a scientific

literature study, focusing on papers looking at virulence gene dis-

covery, modes of pathogenicity and regulation, and host-pathogen

interactions was conducted. A more in-depth analysis involved

splitting of papers citing mutant collections into twelve different

scientific aspects (

Figure 2

).

The results produced ten relevant mutant screens, a striking

observation of which was that a large number of generated mu-

tant isolates represented only a portion of phenotypically altered

isolates; these phenotypically altered isolates are the very fungal

strains containing mutations in specific genes, while the remainder

of the genome is either uninterrupted or less important for fungal

functions.

However, given that a few mutant isolates were altered, a few

genes responding to different treatments were thus represented

(Table 1). This may be due to dependence on less sensitive pheno-

typic assays and lack of additional phenotypic or in planta screens.

Citations of fungal mutant collections were assessed, the relevance

of which is crucial to see if findings from these collections are

channelled to solve agricultural problems in the South African

context. Interestingly, none of the reports came from South Africa

when a total of 397 citing papers, 116 citing

F. graminearum

mutant

screens and 281 citing

M. oryzae

mutant screens (Figure 2), were

screened.

Therefore, there is a huge gap to generate and screen fungal mu-

tant collections in South Africa. Ultimately, performing such

mutant screens, more in particular for

F. graminearum

, will drive

the identification of virulence genes relevant to crops in this

country. Furthermore, increasing the number of genes and related

pathways involved in virulence will potentially complement the on-

going breeding efforts made for the South African producer.

To conclude, it is apparent that the application of fungal mutant

collections is still in infancy when it comes to effector search. Only

M. oryzae

targeted gene disruption (TGD) collection provides

screening of effectors. Available transcription factor (TF) mutant

collections can potentially guide the development of alternative and

effective fungicides, which target conserved TF proteins.

Since TFs control multiple genes which influence multiple biologi-

cal processes, associated developmental costs of fungicides which

target these TFs will substantially drop. This is because such fun-

gicides will not be developed for countless downstream genes of

TFs. Disease control procedures should thus unify findings from

effector and TF mutant collections to advanced effector-assisted

breeding and biological control using TFs as potential targets. The

prospect of making collections of mutants for the South African

molecular pathologist is within reach, and will potentially involve

the inclusion to the list of mutant collections of fungi such as

wheat rusts.

Having these genetic resources in the country can greatly facili-

tate and accelerate disease combat efforts as well as significantly

improve crop production and profitability for producers.

For more information, contact Dr Thabiso Motaung at

motaungte@arc.agric.za .