This concerto, preserved at Melk Abbey under Rosetti's name, has until now not been recognised as a concerto for solo horn.
In his thematic catalogue of Rosetti's works, published in 1996, Sterling E. Murray classes it among the concertos for two horns, in which the first solo horn is said to have been lost. How did this assumption arise, given that the title page reads only “Concerto pour le cor”? The reason is found in the solo horn part itself. It is marked “Corno 2do Prinzipale in Dis”, which easily raises the question of the “Corno 1do”, as if this were an incomplete double horn concerto with a missing first horn part.
The right approach, however, is probably to take a closer look at the supposed second solo horn part. On going through and playing the part, I very quickly established that this second horn part is by no means incomplete and that no first horn is missing.
In Rosetti's time at the Wallerstein court there were two gifted horn players, Joseph Nagel and Franz Zwierzina. Zwierzina's estate contains solo and double horn concertos composed for them by Rosetti, but also by other composers, for example the two concertos for two horns by Hoffmeister edited here. In these concertos, as well as in Rosetti's often equally virtuosic wind-band music for horns, Franz Zwierzina evidently showed unusual skill on the low horn as well.
A solo concerto for horn was regarded (and still is today) as a concerto for the first horn player. Rosetti seems to have composed a solo concerto of his own for Zwierzina or another low horn player. To distinguish them, these concertos for low horn were titled “Concerto for Corno 2do principale”, exactly like the second horn of the double horn concertos. Confusing the two without looking at the musical text is therefore quite understandable.
I also consider the doubtful attribution of authorship to be rather unlikely. The proof is found in the horn part itself: in bars 84–87 the humorous Rosetti quotes, with Bohemian wit, the theme of the double horn concerto in E-flat major by his orchestral colleague Joseph Fiala, who likewise came from Bohemia. Together with Fiala, Rosetti began his service with Prince Kraft Ernst in Wallerstein in 1773. The horn soloist surely knew this concerto and enjoyed the secret quotation.