自民國六十七年九月起，至六十九年二用底止，在本省各木瓜發病地區採回病徵型不同之230 個標本，經寄主範圍測定，得知採回的木瓜病葉可感染南瓜、西瓜等葫蘆科作物，在藜產生局部斑點，而不感染千日紅、大豆、菸草等，應屬於木瓜輪點病毒(PRSV)。
經藜上之單一斑分離三代而得到純病毒分離株，依木瓜上產生不同的病徵型，判別為三系統︰壞疽嵌紋系統(SMN)， 產生嚴重嵌紋與壞疽以至全株萎凋；嚴重嵌紋系統(SM)，葉片產生嚴重嵌紋病徵；嵌紋系統(M)， 葉片產生輕微嵌紋。SM型頻度最高(50.9%)，SMN型次之(41.5%) M型最少(7.6%)。
這些輪點病毒系統可在藜上產生兩種不同局斑型，黃化局斑型(Chlorotic locallesion) 與壞疽局斑型(Necrotic local lesion)， 壞疽局斑型系統可使木瓜產生萎凋，而黃化局斑型系統一群對木瓜，因分離株不同而產生不病徵型，包括上所述三種病徵型。
SM系統與SMN 系統的致死溫度有二種範圍，即50∼50℃與55∼60℃。M 系統之致死溫度在55∼60℃，各系統經電子顯微鏡觀察，皆可看到666∼726mm之絲狀病毒顆粒。在SM系統中之分離株，在南瓜上分為形成葉脈透化嵌紋型(VC)與葉脈黃化壞疽型(VN)兩種病徵之分離株系，兩種病徵型株系經南瓜再接回木瓜亦產生SM型嚴重嵌紋病徵。
就病毒系統在木瓜體中之增殖與相互作用(Interaction)，M系統的增殖速率與移動速率均慢、細胞中之病毒含量亦低。SM系統的增殖速率與移動速率亦慢，但病毒在木瓜體中含量則高，而SMN 系統的病毒除濃度高外，其移動速率亦快，故SMN 系統在木瓜中15天，病毒含量即可達高峰，而SM系統在25天，M 系統在27天方達高峰，在高峰期，SM系統與SMN 系統的濃度大致相等，而M 系統的病毒濃度只有兩系統的一半。
木瓜苗齡期愈長，發病潛伏期愈長，但因病毒系統而異。強系統(SMN) 比弱系統(SM,M)短，對2 個月苗前者5 天，後者20天而對6 個月苗前者10天，後者即60天左右。病徵發展受溫度影響，26℃以下時容易呈現病徵，而超31℃時開始隱蔽，SMN系統受溫度之影響較小。
強弱兩系統(M,SMN) 混合感染時病徵發展受兩系統濃度比率所影響，M
弱系統對強系統之交叉保護效果顯著，但不同系統分離株之組合間效果程度有差異，M 系統對SM及SMN 系統效果不完全而SM系統對SMN 系統為完全。交叉接種時間間隔亦影響保護效果，間隔在3 天以下時效果低或無效，一星期以後已有相當效果，但仍不完全。同葉交叉接種比異葉交叉接種有效，但相隔時間2 星期時，異葉交叉接種一樣完全有效。
交叉接種於木瓜之二弱強系統在寄主中之消長，因交叉系統組合而略異，M 系統(PV-TK-11)對SMN 系統(PV-TC-12)交叉保護後50天，M
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During the period from September, 1978 to February, 1980, 230 disease samples of different symptom types were collected form papaya growing areas in Taiwan. The causal virus was identified to be papaya ringspot virus according to the host range test whcih showed systemic infection to cucurbitaceous plants such as squash, watemelon in addition to papaya, and local lesion formation in Chenopodium amaranticolor, but no infection to Gomphrena globosa, soybean and Nicotiana rustica.
Through 3 successive isolations of single local lesions formed in C. amaranticolr or C. quinoa, the following three strains of different symptom types were obtainedL SMN strain, inducing severe mottling with necrosis and wilting; Sm strain, causing severe mottling; and M strain ; mild mottling. the frequency of SM strain was hightest (50.9%), SMN strain (41.5%) came to the next, and that of M strain was lowest (7.6%).
The virus isolated induced two different locallesion types , of chlorotic local lesion (CLL) and necrotic local lesion (NLL) in Chenopodium amaranticolor. The isolates of NLL type produced symptoms of SMN strain, and CLL isolates included the 3 strains mentioned above. Such two different symptom as mild mottling with vein clearing (VC) and vein yellowing with vein necrosis (VN) were differentiated among the isolates of SM strain by squash inoculation. Both SM and SMN strains included two different thermal inactivation point, 50-55℃ and 55-60℃, while m strain had a TIP of 55-60℃. Electron micrograph showed the three strains of PRSV with filamentous virus particles about 666 to 726 nm long.
SMN strain multiplied and moved systemically upward to plan top most rapidly, and its concentration declined fast in papaya plants. The multiplication rate of SM strain was the second, and M strain increased slowest in papaya plants. Both SM and M strains moved more slowly than SMN strain. Concentration of SM strain declined faster than M strain which maintained certain level of concentration much longer than the former strain.
The incubation period of papaya seelings infected with PRSV, was affected by plant age and different virus strains, i.e. 5 days shown by virulent strain (SMN), and 20 days by milder strains (SM and M) in 2 month old seedlings; while 10 days by SMN and about 60 days by SM or M strain in 6 month old seedlings. The symptoms developed easily around 26℃, but became masked at temperature over 31℃. symptom development of SMN strain was affected by temperature a little.
The symptom types of papaya plants infected with a mixture of virus strains were varied by concentration ratio of the two strains, namely intermediate symptom type (SM) developed in the plant inoculated with a mixinocula at 1:10-2 of M
In papaya plants mix-inoculated with CLL- and NLL-type isolates, CLL-type isolate dominated over NLL-type, and titer of the former was 4 times more than that of the latter. The CLL isolate interfered the infection of immediate follower inoculum of NLL isolate, however no interaction was demonstrated in case of the reverse inoculum order in Chenopodium amaranticolor.
The effectiveness of cross protection with mild strain against severe strains was prominent, but differed with different combinations among strains. The combinatins of protective M strain against challenging SM or SMN strains, showed incomplete effectiveness, while SM strain completely protected papaya plants against infection with SMN strain. The cross protection was also affected by tim intervals between cross inoculations, i.e. no or a little effectiveness was demonstrated in case of 3 days interval, and ignificant protection was found at interval over 1 week.Cross inoculation made in the same leaf showed more prominent protect0ion than that of cross inoculation in different leaves, but almost similarly complete protection was experienced in the both inoculation loci at cross interval over 2 weeks.
The titer dynamic of 2 strains in cross-inoculated papaya plants, was varied by different combinations of 2 cross strains. The isolation ratio of M

SMN 比在１：１０-2 時呈中間型病徵(SM)而１：１或１０-1時強系統佔優勢呈SMN 型病徵。黃化局斑型(CLL) 與壞疽局斑型(NLL) 二分離株混合感染時，CLL 型比NLL 型佔優勢，接種後25天時前者比後者之濃度高四倍以上。在藜前後接種，CLL 型分離株對後接NLL 型系統有阻礙感染作用，但後者對前者即無相互干擾作用。

SMN 之分離比為9:1。 CLL局斑型之M 系統(PV-TT-1-m) 對NLL 局斑型之SMN 系統(PV-TN-5)， 在交叉接種後17天CLL 對NLL 出現比為124:1， 但22天後NLL 型不再分離到，其交叉效果為完全。

SNMN ratio, but symptom type of SMN dominated in plants inoculated with inoculum mixtures at 1:1 or 1:10-1 ratio.

SMN strains was 9:1 in a papaya plant protected with M strain (PV-TK-11) against SMN strain (PV-TC-12) 50 days after challenging inoculation. A number ratio, 124:1 of CLL to NLL local lesion types appeared in Chenopodium leaves assayed with tissue samples collected from papaya plants cross-inoculated with M strain of CLL type against SMN strain of NLL type 17 days after challenging inoculation, was obtained, but no NLL type local lesion was detected 22 days later.