The affix matup comes in the sense of 'whose it is' or 'in whom it is' after the prātipadika (Nominal Stem) rasa etc.,
As रसवान्, रूपवान्, गन्धवान् ॥ Why this special sutra with regard to रसादि words, when they would have taken मतुप् by the last sutra? This prevents the application to these words of other affixes having the sense of मतुप् ॥ How do you form then रूपिणी कन्या, रूपिको दारकः ॥ These are rare forms. According to Patanjali this sutra is useless. Or the word रस &c, must denote qualities, perceivable by the organs of taste, touch &c, i. e. रस should mean taste, रूप form. Therefore the forms रूपिणी and रूपिकः are valid, meaning शोभायोग्यता ॥ So also रसिको तटः = भावयोगः, here रूप and रस do not mean 'form' and 'taste'. And all words of quality having one syllable are governed by this sutra, and form their derivative in मतुप् ॥ See 5.2.115.
1 रस, 2 रूप, 3 वर्ण, 4 गन्ध, 5 स्पर्श, 6 शब्द, 7 स्नेह, 8 भाव, 9 गुणात्, (गुणग्रहणं रसादीनां विशेषणम्), 10 एकाचः (स्ववत्) ॥,