Hi: If you want to identify the Fusarium  spp on Lab level you should to grow tissue on PDA 25C for 3-5 day, you should see the spores under microscope.

For the field identify, wilt symptoms start from the old leaf with yellowish color.

http://www.fao.org/fileadmin/templates/banana/documents/Docs_Resources_2015/TR4/2-banana-fusarium-wilt.pdf  

Dear Dr R Einstein Charles

Pls. find the attached files

https://www.omicsgroup.org/journals/diversity-and-distribution-of-the-banana-wilt-pathogen-fusarium-oxysporum-f-sp-cubense-in-china-2165-8056.1000111.php?aid=22205

http://www.publish.csiro.au/cp/AR9960637

http://www.promusa.org/Fusarium+wilt

http://www.ishs.org/ishs-article/897_46

http://www.cabi.org/isc/datasheet/24621

http://www.academia.edu/25191678/Molecular_and_Biochemical_Detection_of_Fusarium_Oxysporum_f.sp._cubense_as_the_Pathogen_of_Fusarium_Wilt_Disease_on_Banana_Musa_spp._

http://www.jnsci.org/files/html/2016/e239.htm

https://www.researchgate.net/publication/227617318_A_molecular_diagnostic_for_tropical_race_4_of_the_banana_fusarium_wilt_pathogen

Hoping this will be helpful

Regards

Prof. Houda Kawas

Article A molecular diagnostic for tropical race 4 of the banana fus...

Dear , Dr R Einstein Charles.

If you want to identify Fusarium you should apply the following steps:

1 - Bring portions from the infected plants to the laboratory .

2 - Cutting these plants to a small parts ( 1 - 2 ) cm.

3 - Washing the plant parts with tap water.

4 - Sterilize them with Sodium Hypochlorite for 2 minuets , then washing them with sterile distilled water.

5 - Putting them in Petridishes containing PDA and incubating them for 3 - 4 days at 25 oc.

6 - Preparing slides with lactophenol.

7 - Testing the macro and micro features by observe the colony shape , color and diameter . 

8 - Noticing the phialides   if they are mono or poly phialides.

9 - Noticing macro , micro and chlamydo conidia, if they are found , abundant , rare or absent. Also the microconidia in false heads or no.

10 - Measuring the macroconidia and noticing there shapes and the number of septa.

With my best regards

Dear , Dr R Einstein Charles.

You can also see the following items.

Best greetings

72

Hi Dr R Einstein Charles

You take samples (root, stem, and corm) from banana that shows wilt symptom as yellowing the old leaf, then 1) cut the samples small piece 1-2 cm, 2) washing and sterilize, 3) put on PDA media, 4) checking after 3 days, 5) do microscope slide and check the conidia and phialides (Must be monphialide of F. oxysporum)

Good Luck

Thank you Dr. R Einstein Charles for up-voting and I hope you have a good luck and more progress in your job.

With my best greetings 

Thank you all for your answers. I need narrow technique to Identify Fusarium on field itself  

Dear , Dr R Einstein Charles.

Fusarium oxysporum f.sp. cubense which caused wilting on banana distinguished by the following features :

1 - Colonies on PDA white , pale salmon or pale mauve or violet , often with salmon or orange sporodochia ; reverse pale salmon and mauve in the center, violet or greyesh.

2 - Macroconidia slightly curved with 3 septa with foot - shaped basal cells .

3 - Microconidia abundant  , fusiform to kidney shaped , produced in false heads from short stout monophialides.

4 - Chlamydospores produced singly or in pairs.

Best regards

Dear , Dr R Einstein Charles.

 The symptoms on the bananas in the field represented by the following :

1 - The external symptoms include chlorosis  yellowing and death the oldest leaves.

2 - The internal symptoms include brown  to red discoloration of the vascular system which range from discrete dots to large areas . 

With best greetings

Dear

You may try the same as similar method we use

for Field evaluations, the symptoms on cutting longitudinal or horizontal of stem bases and incidental, variegated or dark brown color with or without scent enough to distinguish symptoms of fungal, bacterial and viruses . symptoms on the leaves and vegetative growth,  distance between internodes in plants such as chickpeas and cotton.. other crops, and we usually used a degree for resistant or tolerance to differentiate between cultivars, also the patches distribution in the fields. but in banana I did not test them in the field .

Pls. find the attached files, look at page 117,  in downloadPDF.pdf  

Pls. find the attached files

https://www.daf.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/cotton/disease-management/fusarium-wilt

Hoping this will be helpful

Regards

Prof. Houda Kawas

Hi Dr. R Einstein Charles

You can know the type of isolates by pathogenicity test